Film bulk acoustic-wave resonator and method for manufacturing the same

ABSTRACT

A film bulk acoustic-wave resonator having, a substrate having a cavity, the substrate being formed of one of semi-insulating material and high-resistivity material, a bottom electrode partially fixed to the substrate, part of the bottom electrode is mechanically suspended above the cavity, a piezoelectric layer disposed on the bottom electrode, the shape of the piezoelectric layer is defined by a contour, a top electrode on the piezoelectric layer, a semiconductor intermediate electrode buried at and in a surface of the substrate, being located at the contour of the piezoelectric layer, the semiconductor region having a lower resistivity than the substrate, the intermediate electrode is connected to the bottom electrode in the inside of the contour, and a bottom electrode wiring connected to the semiconductor intermediate electrode extending from the contour to an outside of the contour in the plan view.

CROSS REFERENCE TO RELATED APPLICATION AND INCORPORATION BY REFERENCE

This application is a divisional and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. application Ser. No. 11/108,671 now U.S.Pat. No. 7,187,253, filed Apr. 19, 2005 and claims benefit of priorityunder 35 USC 119 based on Japanese Patent Application No. P2004-124774filed Apr. 20, 2004, and Japanese Patent Application No. P2005-99911filed Mar. 30, 2005. The entire contents of these applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a film bulk acoustic-wave resonator(FBAR) using longitudinal vibration mode along a thickness direction ofa piezoelectric layer, and a method for manufacturing the FBAR.

2. Description of the Related Art

Recent wireless communication technology has accomplished rapiddevelopment, and various approaches for achieving a high-speedtransmission are developing more and more. The move to higher operationfrequencies of communication devices has been motivated by the need forlarger and larger data rate, and in addition, there is a great demandthat high frequency communication devices should be fabricated intolighter and smaller geometries. Each of such wireless communicationdevices encompasses a radio frequency (RF) front-end unit, whichprocesses radio frequency signal, and a base-band (BB) unit, whichprocesses digital signal. In the two units, the BB unit modulates anddemodulates signals by digital signal processing architecture and can beeasily miniaturized, since the circuitry for the BB unit can bemonolithically integrated in a single LSI chip. The circuitry for the RFfront-end unit, however, is difficult to be merged into a single LSIchip, since the RF front-end unit must amplify high frequency analogsignals and convert frequency in a high frequency band, therefore the RFfront-end unit requires a complicated configuration, which includesoscillators and many and various passive components such as filters.Generally, a surface acoustic wave (SAW) device is used as an elementfor RF filters and IF filters in mobile communication devices of earliertechnology. However, since resonance frequency of the SAW device isinversely proportional to a spacing between comb-shape electrodes, infrequency band exceeding 1 GHz, the spacing between comb-shapeelectrodes becomes 1 μm or less, it is difficult to meet the demand forhigher frequency of operation, and the frequency increases higher andhigher, recently. Because the configuration with the SAW device isassembled by discrete components, for instance, special substrates suchas lithium tantalate (LiTaO₃), the RF front-end unit is not suitable forminiaturization.

For a substitute of the SAW device, as a resonator, which attractsattention recently, there is a FBAR using longitudinal vibration modealong a thickness direction of a piezoelectric layer. The FBAR is called“bulk acoustic wave” (BAW) element, etc. Because, in the FBAR, theresonance frequency is determined by acoustic wave velocity and filmthickness of the piezoelectric layer, the resonance frequency is about 2GHz at a film thickness of one to two μm and is about 5 GHz at a filmthickness of 0.4 to 0.8 μm. Therefore, the FBAR facilitates highfrequency operations up to several decades GHz. As the FBARs arecomparatively easy to fabricate on a silicon (Si) substrate, the FBARsare advantageous for miniaturization of the wireless communicationdevices.

A representative structure of the FBAR of earlier technology has beendisclosed in Japanese Published Unexamined Patent Application No.2000-69594. As shown in the Japanese Published Unexamined PatentApplication No. 2000-69594, the FBAR is manufactured by the followingformation process sequences. First, a cavity is formed on a Si substrateby anisotropic etching, and next, a sacrificial layer such asboro-phosphate-silicate-glass (BPSG), which is easily etched by aspecific etchant, is buried in the cavity at the top surface of thesubstrate. Afterwards, the sacrificial layer is polished flat until thetop surface of the Si substrate is exposed. By the process, thesacrificial layer is embedded in the cavity at the top surface of the Sisubstrate and the surface of the Si substrate surrounds the perimeter ofthe sacrificial layer. On the sacrificial layer, a bottom electrode, apiezoelectric layer and a top electrode are deposited successively.Afterwards, an etchant supplying conduit is excavated until theetchant-supplying conduit reaches the top surface of the sacrificiallayer. Then, the sacrificial layer is removed by selective etching withetchant supplied through the etchant supplying conduit, and a cavity isselectively formed under the bottom electrode. By such a sequence offormation processes, the FBAR is completed.

According to the manufacturing method of the FBAR disclosed in JapanesePublished Unexamined Patent Application No. 2000-69594, the sacrificiallayer is formed at the top surface of the Si substrate, and the bottomelectrode is formed on the Si substrate so as to cover the sacrificiallayer, and further, on the top surface of the bottom electrode, apiezoelectric layer is stacked. Then, the piezoelectric layer isdelineated to occupy a given limited area, and the top electrode isdelineated on the piezoelectric layer. In the sequence of formationprocesses, after the piezoelectric layer is delineated, a pattern of anextraction wiring of the bottom electrode is delineated by wet etchingusing such solutions as potassium hydroxide (KOH), tetra methyl ammoniumhydroxide (TMAH), for instance, or dry etching such as reactive ionetching (RIE) method. Aluminum nitride (AlN), or alternatively zincoxide (ZnO) is generally adopted for material of the piezoelectric layerand especially AlN is widely used because of the material behavior thatfacilitates the matching with the semiconductor manufacturing processes.

However, there are problems in that in either case of using AlN or ZnO,the etching rate of the piezoelectric dielectric film is low andsufficient etching selectivity of the piezoelectric dielectric film to ametallic film for the bottom electrode is hard to be achieved, when thepiezoelectric dielectric film is selectively etched to expose the bottomelectrode so that the extraction wiring can be connected to the bottomelectrode. When the etching selectivity of the piezoelectric dielectricfilm to a metallic film for the bottom electrode is not sufficient, anover-etching for assuring uniformity of the etching depth decreases thefilm thickness of the bottom electrode in part of an element region orover the whole element region. Then, series resistance of the bottomelectrode increases and contact resistance between the extraction wiringand the bottom electrode increases due to surface roughness anddegeneration of the bottom electrode.

As parameters representing resonance characteristic of the FBAR,electromechanical coupling factor k_(t) ², which is an indicator of theeffectiveness with which a piezoelectric material converts electricalenergy into mechanical energy, or converts mechanical energy intoelectrical energy and Q-value, which is a measure of the sharpness ofthe resonance peak in the frequency response of the system, areemployed. There are two Q-values; one is a Q-value at a resonancefrequency in which electrical impedance becomes a minimum and another isa Q-value at an anti-resonance resonance frequency in which theelectrical impedance becoming a maximum. When a filter is implemented bya combination of resonators, a frequency bandwidth of the filter isproportional to the electromechanical coupling factor k_(t) ², andinsertion losses in the subject frequency band are inverselyproportional to a quality factor defined by product of the Q-value andthe electromechanical coupling factor k_(t) ². Since theelectromechanical coupling factor k_(t) ² is a value proper to material,there is no necessity for increasing the electromechanical couplingfactor k_(t) ², if an appropriate frequency bandwidth can be realized byimproving crystal purity and controlling crystal orientation to apolarization direction. Therefore, the Q-value must be set as high aspossible so as to decrease the insertion losses.

Elastic loss of the piezoelectric layer, elastic loss of the electrode,and series resistance of the electrode affect the Q-value at resonancefrequency and the elastic losses of the piezoelectric layer, the elasticlosses of the electrode, conductance of the substrate, and dielectriclosses of the piezoelectric layer affect the Q-value at anti-resonancefrequency. According to analysis of experimental data of inventors ofthe present invention, series resistance of the bottom electrode play adominant role as the origin of degradation of the Q-value at resonancefrequency, and elastic losses of the piezoelectric layer is the dominantorigin of degradation of the Q-value at anti-resonance frequency. Fromthe investigation, an increase of series resistance of the bottomelectrode by etching failure, causes the degradation of the Q-value atresonance frequency, which greatly affects performances of the FBAR. Inaddition, e investigation proved a possibility in which disconnection ofthe bottom electrode is caused by over-etching.

So to overcome the above-mentioned problems due to over-etching, variousmethodologies such as:

(a) selecting material of the bottom electrode so that etchingselectivity of the piezoelectric dielectric film to a metallic film forthe bottom electrode is sufficiently large (hereinafter called “thefirst methodology”);

(b) providing some margins for over-etching by increasing the filmthickness of the bottom electrode (hereinafter called “the secondmethodology”); and

(c) decreasing etching rate of the piezoelectric dielectric film so asto facilitate detecting the end point of the etching (hereinafter called“the third methodology”), are adopted.

However, in the first methodology, if a high selectivity is required asone of the specific material properties so as to overcome the problemsassociated with the low etching selectivity, freedom for selectingmaterials becomes small, because the material property must satisfy therequired low resistance value and low elastic losses (internalfriction), etc. Because the thickness of the bottom electrode has greateffect upon the resonance characteristic itself, there is an optimumfilm thickness of the bottom electrode. If the thickness of the bottomelectrode cannot satisfy the optimum film thickness, theelectromechanical coupling factor k_(t) ², which is an index to theintensity of the piezoelectricity, decreases, and further the Q-value,which is a measure of the sharpness of resonance peak in the frequencyresponse of the system, decreases, and still further shift of theresonant frequency is generated. Therefore, the second methodology suchthat providing some margins for the etching process, by increasing thefilm thickness of the bottom electrode so as to overcome problemsassociated with over-etching of the bottom electrode has a limitation.Further, by the third methodology, decreasing the etching rate of thepiezoelectric dielectric film so as to facilitate detecting the endpoint of the etching process, the processing time for each etchingprocess becomes long, which increases the throughput time.

In view of these situations, it is an object of the present invention toprovide a FBAR, which has a large electromechanical coupling factork_(t) ² and a large Q-value, and a method for manufacturing the FBAR.

SUMMARY OF THE INVENTION

An aspect of the present invention may inhere in a film bulkacoustic-wave resonator encompassing (a) a substrate having a cavity,(b) a bottom electrode partially fixed to the substrate, part of thebottom electrode is mechanically suspended above the cavity, (c) apiezoelectric layer disposed on the bottom electrode, a planar shape ofthe piezoelectric layer is defined by a contour, which covers an entiresurface of the bottom electrode in a plan view, (d) a top electrode onthe piezoelectric layer, (e) an intermediate electrode located betweenthe substrate and the piezoelectric layer, and at the contour of thepiezoelectric layer, the intermediate electrode is connected to thebottom electrode in the inside of the contour, and (f) a bottomelectrode wiring connected to the intermediate electrode extending fromthe contour to an outside of the contour in the plan view, wherein alongitudinal vibration mode along a thickness direction of thepiezoelectric layer is utilized.

Another aspect of the present invention may inhere in a film bulkacoustic-wave resonator encompassing (a) a substrate having a cavity,the substrate being formed of one of semi-insulating material andhigh-resistivity material, (b) a bottom electrode partially fixed to thesubstrate, part of the bottom electrode is mechanically suspended abovethe cavity, (c) a piezoelectric layer disposed on the bottom electrode,the shape of the piezoelectric layer is defined by a contour, (d) a topelectrode on the piezoelectric layer, (e) a semiconductor intermediateelectrode buried at and in a surface of the substrate, being located atthe contour of the piezoelectric layer, the semiconductor region havinga lower resistivity than the substrate, the intermediate electrode isconnected to the bottom electrode in the inside of the contour, and (f)a bottom electrode wiring connected to the semiconductor intermediateelectrode extending from the contour to an outside of the contour in theplan view, wherein a longitudinal vibration mode along a thicknessdirection of the piezoelectric layer is utilized.

Still another aspect of the present invention may inhere in a method formanufacturing a film bulk acoustic-wave resonator including (a) formingan intermediate electrode on a substrate, (b) forming a bottom electrodeon the substrate, the bottom electrode is connected to the intermediateelectrode, (c) forming a piezoelectric layer on the bottom electrode andon the intermediate electrode, such that a contour of the piezoelectriclayer covers an entire surface of the bottom electrode in a plan view,and the contour passes on the intermediate electrode, (d) forming a topelectrode on the piezoelectric layer, and (e) forming a bottom electrodewiring connected to the intermediate electrode, the bottom electrodewiring extending from the contour of the piezoelectric layer to anoutside of the contour in the plan view.

Yet still another aspect of the present invention may inhere in a methodfor manufacturing a film bulk acoustic-wave resonator including (a)forming an semiconductor intermediate electrode on a semiconductorsubstrate, the semiconductor intermediate electrode having a lowerresistivity than the semiconductor substrate, (b) stacking a metallicfilm for forming a bottom electrode on the entire surface of thesemiconductor substrate so as to include the semiconductor intermediateelectrode, (c) stacking a piezoelectric dielectric film on the entiresurface of the bottom electrode and on the semiconductor intermediateelectrode, (d) delineating the piezoelectric dielectric film and themetallic film with an identical etching mask so as to form thepiezoelectric layer and the bottom electrode, the piezoelectric layerhas the same shape and the same size as the bottom electrode in a planview, the bottom electrode is connected to the semiconductorintermediate electrode, (e) forming a top electrode on the piezoelectriclayer, and (f) forming a bottom electrode wiring so as to be connectedto the semiconductor intermediate electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view of a film bulk acoustic-wave resonator(FBAR) according to a first embodiment of the present invention;

FIG. 1B is a schematic cross sectional view of the FBAR according to afirst embodiment, taken on line IB-IB in FIG. 1A;

FIG. 2A is a process flow cross sectional view showing an intermediateproduct of the FBAR taken on line IB-IB in FIG. 1A, explaining amanufacturing method of the FBAR according to the first embodiment;

FIG. 2B is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the first embodiment afterthe process stage shown in FIG. 2A;

FIG. 2C is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the first embodiment,after the process stage shown in FIG. 2B;

FIG. 2D is a further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the firstembodiment after the process stage shown in FIG. 2C;

FIG. 2E is a still further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the firstembodiment after the process stage shown in FIG. 2D;

FIG. 3 is a schematic cross sectional view of the FBAR according to amodification of the first embodiment, corresponding to the cross-sectiontaken on line IB-IB in FIG. 1A;

FIG. 4 is a schematic cross sectional view of the FBAR according to acomparative example of the first embodiment, corresponding to thecross-section taken on line IB-IB in FIG. 1A;

FIG. 5A is a process flow cross sectional view showing an intermediateproduct of the FBAR corresponding to a cross-sectional view taken online IB-IB in FIG. 1A, explaining a manufacturing method of the FBARaccording to a comparative example of the first embodiment;

FIG. 5B is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the comparative example ofthe first embodiment after the process stage shown in FIG. 5A;

FIG. 5C is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the comparative example ofthe first embodiment, after the process stage shown in FIG. 5B;

FIG. 5D is a further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to thecomparative example of the first embodiment after the process stageshown in FIG. 5C;

FIG. 5E is a still further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to thecomparative example of the first embodiment after the process stageshown in FIG. 5D;

FIG. 6 is a schematic circuit diagram illustrating an example of a micromechanical filter implemented by a plurality of FBARs of the firstembodiment of the present invention;

FIG. 7 is a schematic circuit diagram illustrating an example of avoltage-controlled oscillator (VCO) implemented by the FBAR of the firstembodiment of the present invention;

FIG. 8 is a schematic circuit diagram illustrating an example of areceiver circuit of a portable transceiver implemented by a plurality ofFBARs of the first embodiment of the present invention;

FIG. 9 is a schematic circuit diagram illustrating an example of atransmitter circuit of a portable transceiver implemented by a pluralityof FBARs of the first embodiment of the present invention;

FIG. 10 is a schematic cross sectional view of the FBAR according to asecond embodiment, corresponding to the cross-sectional view taken online IB-IB in FIG. 1A;

FIG. 11A is a process flow cross sectional view showing an intermediateproduct of the FBAR taken on line IB-IB in FIG. 10, explaining amanufacturing method of the FBAR according to the second embodiment;

FIG. 11B is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the second embodimentafter the process stage shown in FIG. 11A;

FIG. 11C is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the second embodiment,after the process stage shown in FIG. 11B;

FIG. 11D is a further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the secondembodiment after the process stage shown in FIG. 11C;

FIG. 12 is a schematic cross sectional view of the FBAR according to athird embodiment, corresponding to the cross-sectional view taken online IB-IB in FIG. 1A;

FIG. 13A is a process flow cross sectional view showing an intermediateproduct of the FBAR taken on line IB-IB in FIG. 10, explaining amanufacturing method of the FBAR according to the third embodiment;

FIG. 13B is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the third embodiment afterthe process stage shown in FIG. 13A;

FIG. 13C is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the third embodiment,after the process stage shown in FIG. 13B;

FIG. 13D is a further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the thirdembodiment after the process stage shown in FIG. 13C;

FIG. 13E is a still further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the thirdembodiment after the process stage shown in FIG. 13D;

FIG. 14 is a schematic cross sectional view of the FBAR according to afourth embodiment, corresponding to the cross-sectional view taken online IB-IB in FIG. 1A;

FIG. 15A is a process flow cross sectional view showing an intermediateproduct of the FBAR taken on line IB-IB in FIG. 10, explaining amanufacturing method of the FBAR according to the fourth embodiment;

FIG. 15B is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the fourth embodimentafter the process stage shown in FIG. 15A;

FIG. 15C is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the fourth embodiment,after the process stage shown in FIG. 15B;

FIG. 15D is a further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the fourthembodiment after the process stage shown in FIG. 15C;

FIG. 16A is a schematic plan view of a FBAR according to a fifthembodiment of the present invention;

FIG. 16B is a schematic cross sectional view of the FBAR according to afifth embodiment, taken on line XVIB-XVIB in FIG. 16A;

FIG. 17A is a process flow cross sectional view showing an intermediateproduct of the FBAR taken on line XVIB-XVIB in FIG. 16A, explaining amanufacturing method of the FBAR according to the fifth embodiment;

FIG. 17B is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the fifth embodiment afterthe process stage shown in FIG. 17A;

FIG. 17C is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the fifth embodiment,after the process stage shown in FIG. 17B;

FIG. 17D is a further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the fifthembodiment after the process stage shown in FIG. 17C;

FIG. 17E is a still further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the fifthembodiment after the process stage shown in FIG. 17D;

FIG. 18A is a schematic plan view of a FBAR according to a firstmodification of the fifth embodiment of the present invention;

FIG. 18B is a schematic cross sectional view of the FBAR according tothe first modification of the fifth embodiment, taken on lineXVIIIB-XVIIIB in FIG. 18A;

FIG. 19A is a schematic circuit diagram illustrating an example of amicro mechanical filter implemented by a plurality of FBARs of the fifthembodiment of the present invention;

FIG. 19B is an equivalent circuit diagram of FIG. 19A;

FIG. 20 is an example of an actual plan view of the micro mechanicalfilter shown in FIGS. 19A and 19B;

FIG. 21 is a schematic cross sectional view of the FBAR according to asecond modification of the fifth embodiment, corresponding to thecross-section taken on line XVIIIB-XVIIIB in FIG. 18A;

FIG. 22 is a schematic cross sectional view of the FBAR according to asixth embodiment, corresponding to the cross-section taken on lineXVIIIB-XVIIIB in FIG. 18A;

FIG. 23A is a process flow cross sectional view showing an intermediateproduct of the FBAR, corresponding to the cross-section taken on lineXVIIIB-XVIIIB in FIG. 18A, explaining a manufacturing method of the FBARaccording to the sixth embodiment;

FIG. 23B is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the sixth embodiment afterthe process stage shown in FIG. 23A;

FIG. 23C is a subsequent process flow cross sectional view showing theintermediate product of the FBAR according to the sixth embodiment,after the process stage shown in FIG. 23B;

FIG. 23D is a further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the sixthembodiment after the process stage shown in FIG. 23C;

FIG. 23E is a still further subsequent process flow cross sectional viewshowing the intermediate product of the FBAR according to the sixthembodiment after the process stage shown in FIG. 23D;

FIG. 24 is an example of an actual plan view of the micro mechanicalfilter implemented by a plurality of FBARs according to anotherembodiment of the present invention;

FIG. 25 is a schematic cross sectional view of one of the FBARsaccording to another embodiment, taken on line XXV-XXV in FIG. 24;

FIG. 26 is an example of an actual plan view of the micro mechanicalfilter implemented by a plurality of FBARs according to still anotherembodiment of the present invention; and

FIG. 27 is a schematic cross sectional view of one of the FBARsaccording to the still another embodiment, taken on line XXVII-XXVII inFIG. 26.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be described withreference to the accompanying drawings. It is to be noted that the sameor similar reference numerals are applied to the same or similar partsand elements throughout the drawings, and the description of the same orsimilar parts and elements will be omitted or simplified. Generally andas it is conventional in the representation of acoustic devices, it willbe appreciated that the various drawings are not drawn to scale from onefigure to another nor inside a given figure, and in particular that thelayer thicknesses are arbitrarily drawn for facilitating the reading ofthe drawings.

In view of material properties such as resistivity, elastic constant,and density, materials for top and bottom electrodes of the FBAR aredetermined. Especially, for materials of the bottom electrode, crystalstructure of the bottom electrode material, preferred orientation planeof the bottom electrode material and orientation of the piezoelectricdielectric film must be added as the selection constraints, since thebottom electrode is supposed to serve as an underlying film, whichinfluences the orientation of the piezoelectric dielectric film, whichwill deposit on the bottom electrode. Therefore, materials such astungsten (W), molybdenum (Mo), titanium (Ti), aluminum (Al), ruthenium(Ru), rhodium (Rh), palladium (Pd), iridium (Ir), platinum (Pt) aregenerally used as materials of the bottom electrode.

Through the experimental investigation by inventors of the presentinvention, it is clear that if Al and Ti are used as the bottomelectrode materials, by any methods in wet etchings and dry etchings,the etching selectivity of the piezoelectric layer over the bottomelectrode is low, and therefore, manufacturing margin is very low. Forinstance, when Al is used for the bottom electrode and AlN is used forthe piezoelectric layer, the selectivity, which is defined by:

-   -   (AlN etching rate)/(Al etching rate)        is about 0.5 by dry etching with chloride based etching gas.        When over-etching occurs, since series resistance of the bottom        electrode increases and the Q-value deteriorates, it is        necessary to minimize any decrease in thickness of the bottom        electrode. However, in a case where the selectivity is less than        about 0.5, fluctuation of detection sensitivity in the etching        end point monitoring occurs, and it is difficult to take        sufficient margins for over-etching, and the manufacturing        margin allowed in the process sequence becomes very narrow. For        instance, if an AlN film of 2 μm thickness is used as a        piezoelectric layer, the thickness of the bottom electrode        becomes ½ of the original value by an error in seconds, or the        time interval between the instant at which the etching end point        is detected and the instant at which the etching is actually        stopped, and resistance of the bottom electrode increases over        double of the original value.

With regard to materials such as W, Mo, Ru, Rh, Pd, Ir, Pt, etc.,although the etching selectivity of the piezoelectric layer over thebottom electrode can be ensured to some extent, the film thickness ofthe bottom electrode must be thinned up to under several hundred nm,because specific gravities of W, Mo, Ru, Rh, Pd, Ir, Pt, etc., arelarge. Also, according to the experimental investigation, it turned outthat especially for a resonator operating at higher frequency bands, themanufacturing margin is very narrow, since the resonance characteristicdeteriorates due to the increase of the series resistance of the bottomelectrode, which is caused by localized over-etching. For instance, whenMo film is used as the bottom electrode and operation frequency is over5 GHz, the film thickness of the bottom electrode must be less thanabout 100 nm, resulting in a deterioration of the Q-value by a slighterror of the time interval between the instants at which the etching endpoint is detected and at which the etching is actually stopped.

Therefore, inventors of the present invention repeated a wide range ofvarious experimental investigations over various factors and conditionsso as to specify a best processing condition and a best configuration,in which an increase of resistance in the bottom electrode can not begenerated, when AlN, or alternatively ZnO, serving as the piezoelectriclayer, is processed under a sequence of formation processes. And theinventors concluded that a margin can be expanded and characteristics ofa FBAR can be extraordinarily improved, by forming an intermediateelectrode, which is implemented by an electrically conductive thin film,so that an extraction wiring, configured to connect the bottom electrodeto an external interconnection, can be connected to the intermediateelectrode.

According to the above-mentioned methodology, if the intermediateelectrode formed of electrically conductive material can increase theetching selectivity of the piezoelectric layer over the intermediateelectrode, any material constraints for the bottom electrode and processmargins for the film thickness of the bottom electrode are notnecessary. And, since the film thickness of the intermediate electrodehas no relation with resonator characteristics directly, it is possibleto increase the film thickness of the intermediate electrode.Furthermore, a range of selecting materials for the bottom electrode, inview of resistivity and etching selectivity, etc., can be expanded.Further a margin for instabilities of processes such as fluctuation ofthe processing condition also extends. Therefore, a large technicaladvantage in the manufacturing of the FBAR is achieved by the employmentof the intermediate electrode.

In addition, inventors of the present invention found out that a processmargin extends further, when the intermediate electrode has a specificorientation direction. AlN, or alternatively ZnO has a wurtzite latticestructure and an orientation of the piezoelectric dielectric film itselfis also affected by the orientation direction of an underlying film.When the piezoelectric layer is orientated on the intermediate electrodetoo, a large difference is not shown in the orientations on the bottomelectrode and on the intermediate electrode, and the grain sizes of thepiezoelectric layers are comparatively the same, which can improve filmuniformity of the piezoelectric layer. When film quality of thepiezoelectric layer is not homogeneous, there is a high probability thatcracks at the boundary of the piezoelectric layer may occur,consequently, failures such as film peeling may occur by an effect ofresidual stress.

In the following description specific details are set forth, such asspecific materials, process and equipment in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownmanufacturing materials, process and equipment are not set forth indetail in order not to unnecessary obscure the present invention.Prepositions, such as “on”, “over”, “under”, “beneath”, and “normal” aredefined with respect to a planar surface of the substrate, regardless ofthe orientation in which the substrate is actually held. A layer is onanother layer even if there are intervening layers.

First Enbodiment

A film bulk acoustic-wave resonator (FBAR) according to a firstembodiment of the present invention encompasses a substrate 11 having acavity 18, a bottom electrode, part of which is mechanically suspendedabove the cavity 18 and another part of which is mechanically fixed tothe substrate 11, a piezoelectric layer 15 disposed on the bottomelectrode, a planar shape of the piezoelectric layer 15 is defined by acontour, which covers an entire surface of the bottom electrode in aplan view shown in FIG. 1A, a top electrode 16 on the piezoelectriclayer 15, an intermediate electrode 13 located between the substrate 11and the piezoelectric layer 15, and at the contour of the piezoelectriclayer 15, the intermediate electrode 13 is connected to the bottomelectrode in the inside of the contour, and a bottom electrode wiring 17connected to the intermediate electrode 13 extending from the contour toan outside of the contour in the plan view shown in FIG. 1A. The FBARaccording to the first embodiment further encompasses an insulating film12 inserted between the substrate 11 and the intermediate electrode 13.For materials of the insulating film 12, various dielectric films suchas a silicon oxide film (SiO₂), a silicon nitride (Si₃N₄) film or acomposite film of the silicon oxide film (SiO₂) and the silicon nitride(Si₃N₄) film can be used. However, the insulating film 12 can beomitted, if a high-resistivity or a semi-insulating substrate isemployed for the substrate 11, as shown in FIGS. 14, 16B, 18B, 21, 22and 27. The FBAR according to the first embodiment utilizes alongitudinal vibration mode, or a bulk vibration mode, along a thicknessdirection of the piezoelectric layer 15.

In the plan view shown in FIG. 1A, the contour of the piezoelectriclayer 15 crosses a top surface of the intermediate electrode 13 and partof the intermediate electrode 13 extends to the outside of the contourof the piezoelectric layer 15, from the contour of the piezoelectriclayer 15.

As shown in FIG. 1B, a cross sectional view of the intermediateelectrode 13 is in a trapezoid configuration defined by a first mainsurface disposed near side of the piezoelectric layer 15, a second mainsurface disposed near side of the substrate 11, being opposite to thefirst main surface, the first and second main surfaces are in parallel,and slanted sidewalls intersecting with the second main surface with ataper angle less than 45 degrees, the slanted sidewalls are connectedbetween the first and second main surfaces. A planar shape of theintermediate electrode 13 is a rectangle in a striped configuration anda length of the stripe is wider than the line width of the bottomelectrode wiring 17 as shown in FIG. 1A. One side of the bottomelectrode 14 is disposed on the intermediate electrode 13 and the bottomelectrode 14 and the intermediate electrode 13 are electricallyconnected. Though the top electrode 16 and the bottom electrode wiring17 have an almost equal line width, the line width of the bottomelectrode 14 is wider than the length of the stripe of the intermediateelectrode 13.

In addition, the FBAR according to the first embodiment includes acavity 18, which is an open cavity implemented by a through-holepenetrating the substrate 11, formed along a direction from the bottomsurface of the substrate 11 to the top surface of the substrate 111 forexposing a bottom surface of the bottom electrode 14. As shown in theplan view of FIG. 1A, an area which the cavity 18 occupies, is definedin the inside of the area which the bottom electrode 14 occupies.Further, the area, which the bottom electrode 14 occupies, is defined inthe inside of the contour of the piezoelectric layer 15 in a plan view.In the FBAR shown in FIG. 1, resonance frequency can be determined byadjusting the film thicknesses of the piezoelectric layer 15 and thebottom electrode 14, since the FBAR utilizes a longitudinal vibrationmode along the thickness direction of the piezoelectric layer 15.

The intermediate electrode 13 of the FBAR according to the firstembodiment may have a body-centered cubic (bcc) lattice structure of<110> orientation, a face-centered cubic (fcc) lattice structure of<111> orientation or alternatively a hexagonal close-packed (hcp)lattice structure of <0001> orientation. Examples of metallic materialsformed of the bcc lattice structure of <110> orientation are Ta, Mo, W,etc. Examples of metallic materials formed of the fcc lattice structureof <111> orientation are Cu, Ir, Pt, etc. Examples of metallic materialsformed of the hcp lattice structure of <0001> orientation are Ti, Ru,etc. In addition, for materials of the intermediate electrode 13, W-Taalloy (mole fraction of Ta=0.01-0.5), Mo-Ta alloy (mole fraction ofTa=0.01-0.5), W-Ti alloy (mole fraction of Ti=0.01-0.3), Mo-Ti alloy(mole fraction of Ta=0.01-0.3), Ti-W alloy (mole fraction ofW=0.01-0.1), Ti-Mo alloy (mole fraction of Mo=0.01-0.1), Pt-Ir alloy(mole fraction of Ir=0.01-0.99), etc. may be used. W-Ta alloy and Mo-Taalloy have the bcc lattice structure of <110> orientation, Pt-Ir alloyhas the fcc lattice structure of <111> orientation and Ti alloys such asW-Ti alloy, Mo-Ti alloy, Ti-W alloy and Ti-Mo alloy have the hcp latticestructure of <0001> orientation. However, the intermediate electrode 13may be formed of a mixed crystal, not perfectly establishing a crystalstructure. And for materials of an underlying layer, which is mainlyused as an adhering layer, Ti, or TiN can be employed, on the adheringlayer, above-mentioned various metals, or alternatively above-mentionedvarious alloys may be stacked so as to implement the intermediateelectrode 13.

The metallic intermediate electrode 13 of the FBAR according to thefirst embodiment has a specific orientation, and the metallicintermediate electrode 13 facilitates the matching with <0001>orientation of hexagonal crystal having a wurtzite lattice structure.Therefore, when AlN, or alternatively ZnO having the wurtzite latticestructure are employed to implement the piezoelectric layer 15, anorientation of the piezoelectric layer 15 itself is also affected by theorientation of the metallic intermediate electrode 13 which serves asthe underlying film of the piezoelectric layer 15. Hexagonal crystals ofthe wurtzite lattice structure such as AlN and ZnO are originallysubject to be oriented along the c-axis, therefore, by designating theorientation of the metallic intermediate electrode 13 to the bcc <110>orientation, the fcc <111> orientation, or alternatively the hcp <0001>orientation, the orientation of the piezoelectric layer 15 is easy to beoriented uniformly along the c-axis, namely along the <0001>orientation. In other words, in the FBAR according to the firstembodiment, the orientation of the piezoelectric layer 15 is identicalto the orientation of the metallic intermediate electrode 13. Bycontrolling a polarization direction (orientation) of the piezoelectriclayer 15 to the c-axis, an electromechanical coupling factor k_(t) ² anda Q-value are easy to be ensured. When the piezoelectric layer 15 isorientated along the c-axis on the metallic intermediate electrode 13, alarge difference is not observed in the orientations of thepiezoelectric layer 15 on the bottom electrode 14 and on the metallicintermediate electrode 13, and the grain size of the piezoelectric layer15 is comparatively same on the bottom electrode 14 and on the metallicintermediate electrode 13, which can improve film uniformity of thepiezoelectric layer 15. When film quality of the piezoelectric layer 15is not homogeneous, there is a high probability that cracks at a contourof the piezoelectric layer 15, defining the shape of the piezoelectriclayer 15 may occur, consequently, failures such as film peeling mayoccur by an effect of residual stress.

For material of the metallic intermediate electrode 13 of the FBARaccording to the first embodiment, a metallic film, which includes atleast one of metal selected from a group consisting of Ta, Mo, W, Ni,Co, Cr, Cu, Ti, Ir, Ru and Pt, is preferable in view of resistivity andetching selectivity, etc. Then, from a viewpoint of film uniformity ofthe piezoelectric layer 15, 45 degrees or less is preferable for a taperangle in the slanted sidewall of the metallic intermediate electrode 13in the cross sectional view shown in FIG. 1A, and 30 degrees or less ismore suitable for the taper angle. If the taper angle in the slantedsidewall of the metallic intermediate electrode 13 exceeds 45 degrees,grain boundaries having different orientations from the orientation ofthe piezoelectric layer 15, are generated in a slanting plane at theedge of the metallic intermediate electrode 13, which may also cause thecracks in the contour of the piezoelectric layer 15, defining the shapeof the piezoelectric layer 15. However, if the taper angle in theslanted sidewall of the metallic intermediate electrode 13 becomes below10 degrees, the occupation area by the metallic intermediate electrode13 relatively increases and area efficiency decreases, which does notmeet the demand for miniaturization.

For instance, in a case in which the metallic intermediate electrode 13is formed of a Mo film with a 500 nm film thickness, full width at halfmaximum (FWHM) of the orientation, or the FWHM established in therocking curve of X-ray diffraction is two degrees, which shows that themetallic intermediate electrode 13 formed of the Mo film has a strong Mo<110> orientation. The taper angle in a sidewall face of the metallicintermediate electrode 13 is cut to be 20 degrees by chemical dryetching (CDE). The FBAR having a configuration such that on the metallicintermediate electrode 13 formed of Mo film with a 500 nm film thicknessand on the bottom electrode 14 formed of Al film with a 300 nm filmthickness, the piezoelectric layer 15 formed of AlN film with a 2 μmfilm thickness is stacked, and on the piezoelectric layer 15, the topelectrode 16 formed of Al film with a 300 nm film thickness is stackedand further, the bottom electrode wiring 17 formed of Al film with a 300nm film thickness, is connected to the metallic intermediate electrode13 shows a high resonance characteristic such that the resonancefrequency is 2.0 GHz, the electromechanical coupling factor k_(t) ² is6.5% and the Q-value at the resonance frequency is 900, the Q-value atthe anti-resonance frequency is 800, according to a result of evaluatingby a measurement using a vector network analyzer.

With reference to FIGS. 2A-2E, a sequence of manufacturing processes ofthe FBAR according to the first embodiment is explained. Note that theFBAR of the first embodiment can be manufactured by variousmanufacturing methods including a modification of the first embodiment,other than the sequence of manufacturing processes disclosed by thefollowing example.

(a) First, the substrate 11 such as Si (100) substrate is prepared. Andon the substrate 11, an insulating film 12 is formed by thermaloxidation methods, etc. Further, on the insulating film 12, a metallicfilm which includes at least one of the metals selected from the groupconsisting of Ta, Mo, W, Ni, Co, Cr, Cu, Ti, Ir, Ru and Pt, having a 200to 800 nm film thickness, or preferably a 400 to 600 nm film thickness,is formed using radio frequency (RF) magnetron sputtering, etc.Afterwards, the metallic film is delineated by photolithography andaccompanying CDE method using fluorine based etching gas so as to form apattern of the metallic intermediate electrode 13 having across-sectional structure shown in FIG. 2A. A planar structure of themetallic intermediate electrode 13 may be formed into a striped pattern,for instance as shown in FIG. 1A.

(b) Next, on the insulating film 12 and on the metallic intermediateelectrode 13, a metallic film such as an Al film, having a 150 to 600 nmfilm thickness, or preferably a 250 to 350 nm film thickness, isdeposited using RF magnetron sputtering, etc. And the metallic film isdelineated by photolithography and accompanying reactive ion etching(RIE) method so as to form a pattern of the bottom electrode 14 as shownin FIG. 2B. The bottom electrode 14 may be delineated by RIE method withchloride based etching gas, when the metallic intermediate electrode 13is formed of a Mo film and the bottom electrode 14 is formed of an Alfilm. In the formation process, one of the ends of the bottom electrode14 is stacked on the metallic intermediate electrode 13 so that thebottom electrode 14 electrically connects to the metallic intermediateelectrode 13.

(c) Afterwards, on the bottom electrode 14 and on the metallicintermediate electrode 13, a piezoelectric dielectric film (mothermaterial film) for the piezoelectric layer 15, having a wurtzite latticestructure with a 0.5 to 3 μm thickness is deposited by RF magnetronsputtering method, etc. as shown in FIG. 2C. The thickness of thepiezoelectric dielectric film (mother material film) for thepiezoelectric layer 15 varies by resonance frequencies, and thethickness of the material film may be determined at about 2 μm, if thepiezoelectric dielectric film (mother material film) for thepiezoelectric layer 15 is AlN if the resonance frequency is supposed tobe about 2.0 GHz. And such AlN film is delineated by photolithographyand accompanying RIE method so as to form a pattern of the piezoelectriclayer 15 as shown in FIG. 2D. The AlN film may be selectively etched byRIE method with chloride based etching gas, when AlN is employed as thepiezoelectric dielectric film (mother material film) for thepiezoelectric layer 15 and a Mo film as the metallic intermediateelectrode 13, which serves as an etching stopper layer. The AlN film isdelineated so that one of the sidewall faces of the piezoelectric layer15 may be located on the metallic intermediate electrode 13, and part ofthe metallic intermediate electrode 13 is exposed from the contour ofthe piezoelectric layer 15. And other than Mo, if the metallicintermediate electrode 13 is formed of such electrically-conductivematerials as W, Ru, Rh, Pd, Ir, and Pt, the etching selectivity of thepiezoelectric layer over the metallic intermediate electrode 13 can beincreased and the metallic intermediate electrode 13 serves as theetching stopper layer when the piezoelectric layer 15 is delineated.

(d) Subsequently, a metallic film having a 150 to 600 nm film thickness,or preferably a 250 to 350 nm film thickness, is deposited so that themetallic film can cover the entire surfaces of the piezoelectric layer15, the metallic intermediate electrode 13 exposed from the contour ofthe piezoelectric layer 15, and the insulting film 12. Afterwards themetallic film is delineated by photolithography and accompanyingselective etching so as to form the top electrode 16 and the bottomelectrode wiring 17 as shown in FIG. 2D. The top electrode 16 and thebottom electrode wiring 17 may be delineated by wet etching using suchsolutions as potassium hydroxide (KOH), tetra methyl ammonium hydroxide(TMAH), in a case in which an Al film is used for the metallic film, anAlN film is used for the piezoelectric layer 15 and a Mo film is usedfor the metallic intermediate electrode 13. The bottom electrode wiring17 is electrically connected to the metallic intermediate electrode 13exposed from the contour of the piezoelectric layer 15.

(e) Afterwards, the thickness of the substrate 11 is adjusted to 100 to300 nm, preferably to 150 to 250 nm. For instance, the thickness of thesubstrate 11 is adjusted up to 200 nm by polishing. Afterwards, anetching-mask is delineated on the bottom surface of the substrate 11 byphotolithography. In a case using a Si substrate for the substrate 11,the substrate 11 is etched from the bottom surface by RIE method withfluoride based etching gas, so as to establish the cavity 18 p as shownin FIG. 2E. Afterwards, the insulting film 12 which remains at thebottom of the cavity 18 p, is removed using wet etching along with RIEmethod with fluoride based etching gas, so as to complete the sequenceof formation processes, and the cross-sectional structure shown in FIG.1B is achieved.

Modification of the First Embodiment

FIG. 3 shows a FBAR according to a modification of the first embodimentof the present invention. The FBAR shown in FIG. 3 is similar to theFBAR according to the first embodiment shown in FIG. 1 in that the FBARaccording to the modification of the first embodiment includes asubstrate 11, an insulating film 12 disposed on the substrate 11, abottom electrode 14 and a metallic intermediate electrode 13 disposed onthe insulating film 12, a piezoelectric layer 15 disposed on the bottomelectrode 14 and the metallic intermediate electrode 13, a top electrode16 disposed on the piezoelectric layer 15 and an bottom electrode wiring17 electrically connected to the metallic intermediate electrode 13. Inaddition, the FBAR of the modification of the first embodiment includesan amorphous metallic film 37 under the bottom electrode 14. Theamorphous metallic film 37 is contacted to the first main surface of themetallic intermediate electrode 13 through one of the slanted sidewalls.For materials of the amorphous metallic film 37, such materials as aTa—Al alloy film and a TiB₂ film having a 5 to 100 nm film thickness, orpreferably a 15 to 30 nm film thickness, can be used. Namely, when theamorphous metallic film 37 is disposed between the bottom electrode 14and the insulating film 12, c-axis orientation of an AlN film disposedon the amorphous metallic film 37, is remarkably improved. Compared witha case in which the amorphous metallic film 37 is not inserted, theelectromechanical coupling factor k_(t) ² and the Q-value which affectgreatly performances of the FBAR can be increased when the amorphousmetallic film 37 is deposited. For instance, the Ta—Al alloy film can bedeposited using Ta and Al target and argon gas, at a substratetemperature of room temperature by RF magnetron sputtering, etc. TheTa—Al alloy film can be selectively etched by RIE method with fluorinebased etching gas, such as octafluorocyclobutane (C₄F₈).

Similar to the FIG. 1, a cross sectional view of the metallicintermediate electrode 13 of the FBAR according to the modification ofthe first embodiment is in a trapezoid configuration, a planar shape ofthe metallic intermediate electrode 13 is striped rectangle. One side ofthe bottom electrode 14 is disposed on the metallic intermediateelectrode 13 and the bottom electrode 14 and the metallic intermediateelectrode 13 are electrically connected. In addition, the FBAR accordingto the modification of the first embodiment includes a cavity 18, whichis formed along a direction from the bottom surface of the substrate 11to the top surface of the substrate 11 for exposing a bottom surface ofthe bottom electrode 14.

In the FBAR of the modification of the first embodiment, the amorphousmetallic film 37 is disposed under the bottom electrode 14, so as toform a double-layer structure with the bottom electrode 14. Forinstance, when the bottom electrode 14 is formed of an Al film and theamorphous metallic film 37 is formed of a Ta—Al alloy film, sincespecific gravity of the Ta—Al alloy film is much larger than thespecific gravity of the Al film, and the Ta—Al alloy film is heavierthan the Al film, high frequency characteristic is deteriorated.Furthermore, the high frequency characteristic is deteriorated by theincrease of the film thickness due to the employment of the double-layerstructure. Therefore, high frequency characteristic is further improvedby selectively etching the amorphous metallic film 37 at a portion wherethe bottom surface is exposed in the cavity 18.

Comparative Example of the First Embodiment

FIG. 4 shows a FBAR, which does not include the metallic intermediateelectrode 13, and compares with the FBAR of the first embodiment.Namely, the FBAR according to a comparative example of the firstembodiment encompasses a bottom electrode 14 c formed of an Al film of300 nm film thickness, a piezoelectric layer 15 formed of an AlN film of2 μm film thickness stacked on the bottom electrode 14 c, a topelectrode 16 formed of an Al film of 300 nm film thickness stacked onthe piezoelectric layer 15, and an bottom electrode wiring 17 formed ofan Al film of 300 nm film thickness directly connected to the bottomelectrode 14 c.

In the FBAR of the comparative example of the first embodiment,disconnection of the bottom electrode 14 in an area represented by acircle labeled by B in FIG. 4, is caused by over-etching orafter-corrosion. This disconnection occurs up to 40% of all the failuresof the FBAR. And even if such disconnection does not occur, seriesresistance of the bottom electrode 14 increases by etching failure.

According to the investigation in which resonance characteristic of theFBAR of the comparative example of the first embodiment is examined byusing a vector network analyzer, although the resonance frequencyremains 2.0 GHz, the electromechanical coupling factor k_(t) ² is 5.5%,the Q-value at the resonance frequency decreases to 150, and the Q-valueat the anti-resonance frequency also decreases greatly to 100. And theseries resistance of the bottom electrode 14 c of the FBAR is determinedas becoming over 15 Ω by a parameter fitting methodology.

With reference to FIGS. 5A-5E, a sequence of manufacturing processes ofthe FBAR according to the comparative example of the first embodiment isexplained.

First, as shown in FIG. 5A, on the Si (100) substrate 11 on which theinsulating film 12 is formed by thermal oxidation methods, etc. an Alfilm of a 300 film thickness is formed by RF magnetron sputtering, etc.Afterwards, the metallic film is delineated by photolithography andaccompanying RIE method with chloride based etching gas, so as to form apattern of the bottom electrode 14 c as shown in FIG. 5B. Afterwards, anAlN film for the piezoelectric layer 15 having a 2 μm film thickness, isdeposited by RF magnetron sputtering method, etc, and a pattern of thepiezoelectric layer 15 is delineated as shown in FIG. 5C byphotolithography and accompanying RIE method with chloride based etchinggas. In the process, the etching end point is monitored by plasmaspectroscopy so that there is no interval between the instant at whichthe etching end point where the Al film is exposed on the bottomelectrode 14 c is detected, and the instant at which the etching isactually stopped, which prevents the bottom electrode 14 c fromover-etching. Subsequently, after depositing an Al film of a 300 nm filmthickness, the Al film is delineated by photolithography andaccompanying wet etching using a combination of nitric acid (HNO₃),acetic acid (CH₃COOH), phosphoric acid (H₃PO₄) so as to delineate thetop electrode 16 and the bottom electrode wiring 17c as shown in FIG.5D. Afterwards, the thickness of the Si substrate 11 is adjusted to 200nm by polishing and a etching-mask is delineated on the bottom surfaceof the Si substrate 11 by photolithography and the substrate 11 isselectively etched from the bottom surface by RIE method with fluoridebased etching gas, so as to establish the cavity 18 p as shown in FIG.5E. Afterwards, the insulting film 12 which remains at the bottom of thecavity 18 p, is removed using wet etching by RIE method with fluoridebased etching gas, thereby completing the sequence of formationprocesses of the FBAR of the comparative example of the firstembodiment.

From the comparison between the manufacturing methods of the FBAR of thefirst embodiment and the FBAR of the comparative example shown in FIG.5, according to the manufacturing method of the FBAR of the firstembodiment, by establishing the metallic intermediate electrode 13formed of such materials as W, Mo, Ru, Rh, Pd, Ir, Pt, the etchingselectivity of the piezoelectric layer 15 over the bottom electrode 14can be ensured to some extent. In other words, the metallic intermediateelectrode 13 can serve as the etching stopper indirectly toward thebottom electrode 14 when the pattern of the piezoelectric layer 15 isdelineated. Therefore, there is no possibility that the bottom electrode14 becomes too thin by over-etching and is disconnected byafter-corrosion. And because the structure provided with the metallicintermediate electrode 13 can prevent series resistance of the bottomelectrode 14 from increasing over a designated value by etching failure,the FBAR of the first embodiment can achieve high frequencycharacteristic in frequency band up to GHz.

According to the manufacturing method of the FBAR of the firstembodiment, because the metallic intermediate electrode 13 is formed ofelectrically-conductive materials which have a large etching selectivityover the piezoelectric layer 15, any material constraints for the bottomelectrode 14 and an extra process margin for the film thickness of thebottom electrode 14 are not necessary. And, since the film thickness ofthe metallic intermediate electrode 13 has no relation with resonatorcharacteristics directly, it is possible to increase the film thicknessof the metallic intermediate electrode 13. Furthermore, a range ofselecting materials for the bottom electrode 13, in view of resistivityand etching selectivity, etc., can be expanded. Further a margin forinstabilities of processes such as fluctuation of the processingcondition also extends. Therefore, a large technical advantage in themanufacturing of the FBAR is achieved by the employment of the metallicintermediate electrode 13.

[Micro Mechanical Filter]

FIG. 6 shows an example of a micro mechanical filter implemented by aplurality of FBARs of the first embodiment. A ladder-type filter 41shown in FIG. 6 is arranged so that four FBARs of F₁, F₂, F₃, F₄ areconnected in series and in parallel to each other. With regard to aconfiguration of the ladder-type filter 41 shown in FIG. 6, when theladder-type filter 41 is actually manufactured, various topologies canbe considered. For instance, the ladder-type filter 41 can bemonolithically integrated in an identical substrate. An input portP_(in) shown in FIG. 6 has two terminals 111 and 112 and an upper inputterminal 111 of the input port P_(in) is connected to the top electrode16 of the F₄ and the lower input terminal 112 of the input port P_(in)is connected to the bottom electrode wiring 17 of the F₄. By theconfiguration, the top electrode 16 of the F₄ is connected to the topelectrode 16 of the F₃, and the bottom electrode wiring 17 of the F₃ isconnected to the top electrode 16 of the F₁, and the top electrode 16 ofthe F₂ respectively.

[Voltage-Controlled Oscillator]

Also the FBAR of the first embodiment can be employed in avoltage-controlled oscillator (VCO) of mobile communication devices by acombination of a variable capacitance C2 and an amplifier 105 as shownin FIG. 7. Namely, in FIG. 7, the top electrode 16 of a FBAR 101 isconnected to the variable capacitance C2, and the bottom electrodewiring 17 of the FBAR 101 is connected to a fixed capacitance C1, andfurther the top electrode 16 of the FBAR 101 is connected to oneterminal of a resistance R2. Between the other terminal of theresistance R2 and the bottom electrode wiring 17 of the FBAR 101, aparallel circuit implemented by the amplifier 105 and a feedbackresistance R1 is connected. To an input terminal of the amplifier 105,signal from an output terminal of the amplifier 105 is positivelyfeed-backed by the feedback resistance R1 so that the signal canoscillate at the resonant frequency of the FBAR 101. The variablecapacitance C2 can be formed of a variable capacitance diode(“vari-cap”) so as to adjust oscillating frequency. The variablecapacitance C2, the fixed capacitance C1, the FBAR 101, the resistanceR2, the feedback resistance R1 and the amplifier 105 may be integratedmonolithically in an identical substrate, or alternatively can beintegrated in a hybrid configuration.

[Transceiver]

FIG. 8 shows a receiver circuit 1 of a portable transceiver, whichencompasses a plurality of micro mechanical filters shown in FIG. 6 soas to implement a radio-frequency (RF) filter 41 and anintermediate-frequency (IF) filter 42. The receiver circuit 1 of theportable transceiver shown in FIG. 8 includes the RF filter 41implemented by the micro mechanical filters of FIG. 6, a mixer 48connected with the RF filter 41 and a local oscillator 49 connected withthe mixer 48, as a RF front-end unit. The mixer 48 mixes RF signaldelivered from the RF filter 41, with RF signal delivered from the localoscillator 49, so as to generate, for example, the IF signal rangingform 200 MHz to 500 MHz. The RF filter 41 is connected to a firstantenna 45 and a second antenna 46 through a duplexer (an antennaswitch) 47. Although in FIG. 8, two antennas of the first antenna 45 andthe second antenna 46 are connected, the number of the antenna is notlimited to two.

The RF signal received at the first antenna 45 and the second antenna 46and the RF signal delivered from the local oscillator 49, are mixed inthe mixer 48 and the mixed signal is transmitted to the IF filter 42which is implemented by the micro mechanical filters of FIG. 6. The IFfilter 42 is connected to an amplifier 50, and the amplifier 50 isfurther connected to a receiver LSI chip 3, in which an in-phase(I)/quadrature-phase (Q) demodulation circuit is merged. The receiverLSI chip 3 is connected to an IQ oscillator 57, which is connected to aresonator 58. Through the IF filter 42, difference-frequency between thefrequency of the RF signal received at the first antenna 45 and/or thesecond antenna 46, and the frequency of the RF signal delivered from thelocal oscillator 49, is extracted so as to be converted into the IFsignal. And the IF signal, or the difference-frequency, is amplified andstabilized by the amplifier 50. The IF signal is I/Q modulated by thereceiver LSI chip 3 to I-signal and Q-signal, which are 90 degrees apartin phase. And lower frequencies, such as base-band I-signal andbase-band Q-signal of 10MHz or less, are processed respectively in amixer 51 and in a mixer 52, which are merged in the receiver LSI chip 3.The base-band I-signal and the base-band Q-signal are amplifiedrespectively by an amplifier 53 and by an amplifier 54 and aretransmitted to a base-band filter 43 and a base-band filter 44. Further,the base-band I-signal and the base-band Q-signal which go through thebase-band filter 43 and the base-band filter 44, are converted intodigital signals by an analog-to-digital (A/D) converter 55 and an A/Dconverter 56, and are further delivered to a digital base-band processor(DBBP), the illustration of which is omitted. Namely, the base-band Isignal which is extracted through the base-band filter 43 is convertedto the digital base-band I signal by the A/D converter 55 and isprocessed by the DBBP. Similarly, the base-band Q signal which isextracted through the base-band filter 44 is converted to the digitalbase-band Q signal by the A/D converter 56 so as to be processed by theDBBP.

FIG. 9 shows a transmitter circuit 2 of the portable transceiver. In thebase-band processing unit of the transmitter circuit 2, adigital-to-analog (D/A) converter 65 and a D/A converter 66, whichconvert digital signal of the base-band I-signal and digital signal ofthe base-band Q-signal from the DBBP into analog signal, are provided.By the D/A converter 65 and the D/A converter 66, the digital base-bandI-signal and the digital base-band Q-signal are converted to the analogbase-band I-signal and the analog base-band Q-signal, and are deliveredto an amplifier 88 and an amplifier 89 of a modulator LSI chip 5 througha base-band filter 61 and a base-band filter 62.

The modulator LSI chip 5 encompasses the amplifiers 88, 89 and mixers85, 86 which are connected to the amplifiers 88, 89. In addition, themodulator LSI chip 5 encompasses an oscillator 60 and a phase shifter87. To the mixer 85 and the mixer 86, carrier wave of RF frequency fromthe oscillator 60 is supplied, each phase of the RF frequency is shiftedto 90 degrees by the phase shifter 87. Output of the amplifiers 88, 89is mixed with the carrier wave of the RF frequency from the oscillator60, and is modulated at the mixers 85, 86. The modulator LSI chip 5 alsoencompasses an amplifier 83, which is connected to an output terminal ofthe adder 84. Output of the mixer 85 and the mixer 86 is delivered tothe adder 84, and output of the adder 84 is delivered to the amplifier83. And output of the amplifier 83 is supplied to MMIC 4, whichimplements the RF front-end unit of the transmitter circuit 2. The MMIC4 encompasses a power microwave transistor 81 and a power microwavetransistor 82 connected in series so as to implement a multi-stageamplification. Output of the MMIC 4 is supplied to the first antenna 45and the second antenna 46 through the duplexer (antenna switch) 47,after amplification at RF frequency by the power microwave transistors81, 82.

In the portable transceiver shown in FIG. 8 and FIG. 9, sinceminiaturized micro mechanical filters are used for the RF filter 41 andthe IF filter 42 instead of a LC circuit using a cavity resonator and aninductor, a portable transceiver which is miniaturized to a small andthin shape and operates in a microwave band of about 1 to 5 GHz with alow power consumption, can be achieved. Of course, although the FBARscan implement such filters operating at a low frequency band as thebase-band filters 43, 44 of FIG. 8, or alternatively the base-bandfilters 61, 62 of FIG. 9, etc., it is preferable to use the FBARs in amicrowave band over 300 MHz, especially in a microwave band about 1 to 5GHz in view of excellent high-frequency characteristics of the micromechanical filter shown in FIG. 6.

Second Embodiment

As shown in FIG. 10, a FBAR according to a second embodiment of thepresent invention includes a substrate 11, an insulating film 12 formedon the substrate 11, a bottom electrode 14, one side of which is fixedto the substrate 11 through the insulating film 12 and the other side ofwhich is mechanically suspended above the insulating film 12 through atrapezoidal cavity 19, a metallic intermediate electrode 13, part ofwhich is disposed on one end of the bottom electrode 14 so as to beelectrically connected to the bottom electrode 14, a piezoelectric layer15 disposed on the bottom electrode 14 and part of the metallicintermediate electrode 13, a top electrode 16 delineated on thepiezoelectric layer 15 and a bottom electrode wiring 17 connected to themetallic intermediate electrode 13. FIG. 10 shows a cross-sectional viewof the FBAR of the second embodiment. Since a planar pattern of the FBARis similar to FIG. 1A, the illustration is omitted, the piezoelectriclayer 15 covers the entire surface of the bottom electrode 14 in theinside of the contour of the piezoelectric layer 15, defining the shapeof the piezoelectric layer 15 in a plan view. And similar to the planview shown in FIG. 1A, the contour of the piezoelectric layer 15 crossesa top surface of the metallic intermediate electrode 13 and part of themetallic intermediate electrode 13 extends to an outside of the contourof the piezoelectric layer 15, from a contour of the piezoelectric layer15.

As shown in FIG. 10, the trapezoidal cavity 19 is disposed above a topsurface of the substrate 11. The trapezoidal cavity 19 is a closedcavity, which is defined by a bottom surface of the bottom electrode 14,a slanting plane of the bottom surface of the bottom electrode 14, a topsurface of the insulating film 12 and the other slanting plane formingpart of the bottom surface (belly) of the piezoelectric layer 15. Inother words, the part of the bottom surface (belly) of the piezoelectriclayer 15 is exposed in the trapezoidal cavity 19, at a vicinity of oneof the slanting planes of the trapezoidal cavity 19, and part of thepiezoelectric layer 15 is suspended above the trapezoidal cavity 19.

As shown in FIG. 10, part of the metallic intermediate electrode 13clamber over an end of the bottom electrode 14 so as to establish alevel difference due to a thickness of the bottom electrode. Then, across-sectional view of the metallic intermediate electrode 13 is shapedlike the letter Z, shapes of the both sidewall faces of the metallicintermediate electrode 13 are tapered, similar to the configurationshown in FIG. 1. Similar to the FBAR of the first embodiment, 45 degreesor less is preferable for a taper angle in the slanted sidewall of themetallic intermediate electrode 13 and 30 degrees or less is moresuitable for the taper angle. Although theoretically, the taper angle inthe slanted sidewall of the metallic intermediate electrode 13 can beset below ten degrees, the occupation area by the metallic intermediateelectrode 13 relatively increases and area efficiency decreases. Aplanar shape of the intermediate 13 is a rectangle in a stripedconfiguration similar to FIG. 1A.

The FBAR of the second embodiment shown in FIG. 10 is different from theFBAR of the first embodiment in that the bottom electrode 14 and themetallic intermediate electrode 13 are electrically connected by such aconfiguration that one side of the bottom electrode 14 creeps into theintermediate 13. However, the FBAR of the second embodiment shown inFIG. 10 is similar to the FBAR of the first embodiment in that resonancefrequency can be determined by adjusting the film thicknesses of thepiezoelectric layer 15 and the bottom electrode 14, through utilizing alongitudinal vibration mode along the thickness direction of thepiezoelectric layer 15. Also since the metallic intermediate electrode13 of the FBAR according to the second embodiment may have the bcclattice structure of <110> orientation, the fcc lattice structure of<111> orientation, or alternatively the hcp lattice structure of <0001>orientation, the metallic intermediate electrode 13 has a specificorientation which facilitates the matching with <0001> orientation ofhexagonal crystal having a wurtzite lattice structure. Therefore, whenAlN, or alternatively ZnO having the wurtzite lattice structure isemployed to implement the piezoelectric layer 15, the orientation of thepiezoelectric layer 15 is easy to be oriented uniformly along thec-axis, namely along the <0001> orientation. By controlling apolarization direction (orientation) of the piezoelectric layer 15 tothe c-axis, an electromechanical coupling factor k_(t) ² and a Q-valueare easy to be ensured. Therefore, similar to the FBAR of the firstembodiment, for material of the metallic intermediate electrode 13 ofthe FBAR according to the second embodiment, a metallic film, whichincludes at least one of the metals selected from a group consisting ofTa, Mo, W, Ni, Co, Cr, Cu, Ti, Ir, Ru and Pt, is preferable. Otherstructure and materials are similar to the structure and materialsalready explained in the first embodiment, and overlapping or redundantdescription may be omitted in the second embodiment.

For instance, the FBAR encompassing the metallic intermediate electrode13 formed of Ir film with a 500 nm film thickness, the bottom electrode14 formed of Al film with a 300 nm film thickness, the piezoelectriclayer 15 formed of AlN film with a 2 μm film thickness, the topelectrode 16 formed of Al film with a 300 nm film thickness and thebottom electrode wiring 17 formed of Al film with a 300 nm filmthickness shows excellent resonance characteristics such that theresonance frequency is 2.0 GHz, the electromechanical coupling factork_(t) ² is 6.2%, the Q-value at the resonance frequency is 600, and theQ-value at the anti-resonance frequency is 550, according to anevaluation by a measurement using a vector network analyzer.

With reference to FIGS. 11A-11D, a sequence of manufacturing processesof the FBAR according to the second embodiment is explained. Note thatthe FBAR of the second embodiment can be manufactured by variousmanufacturing methods including a modification of the second embodiment,other than the sequence of manufacturing processes disclosed by thefollowing example.

(a) First, as shown in FIG. 11A, on the Si (100) substrate 11 on whichan insulating film 12 is formed by thermal oxidation methods, etc., a Mofilm having a 0.5 to 2 μm film thickness, or preferably a 0.8 to 1.5 μmfilm thickness, for instance, a Mo film with a 1 μm film thickness isdeposited using RF magnetron sputtering, etc. And the Mo film isdelineated by photolithography and accompanying CDE method with fluoridebased etching gas, so as to form a pattern of a Mo sacrificial layer 21.A planar shape of the Mo sacrificial layer 21 is a rectangular patternin which a branch member of striped configuration is established so thatthe branch member of striped configuration is orthogonal to one of thesides of the rectangular pattern, although the plan view is omitted.More than two branch members may be established to the rectangularpattern.

(b) Next, on the sacrificial layer 21, an Al film, having a 150 to 600nm film thickness, or preferably a 250 to 350 nm film thickness, isdeposited as a piezoelectric dielectric film (mother material film)using RF magnetron sputtering, etc. And the Al film is delineated byphotolithography and RIE method using chloride based etching gas, so asto form a bottom electrode 14. Furthermore, a lift-off pattern ofphotoresist film is delineated by photolithography and an Ir film havinga 200 to 800 nm film thickness, or preferably a 400 to 600 nm filmthickness is deposited on the lift-off pattern by RF magnetronsputtering. And the Ir film is delineated by “lift-off process” throughsubmerging the substrate 11 in N-methyl-2-pyrrolidone (NMP) solution forsixty minutes, so as to remove the lift-off pattern of photoresist andto form a pattern of the metallic intermediate electrode 13 formed ofthe Ir film as shown in FIG. 11B.

(c) Afterwards, as shown in FIG. 11C, on the bottom electrode 14 and onthe metallic intermediate electrode 13, an AlN film, having a 0.5 to 3μm film thickness, is stacked using RF magnetron sputtering, etc. In acase in which the resonance frequency is designated at about 2.0 GHz,the film thickness of the AlN film may be set at about 2 μm. And the AlNfilm is delineated by photolithography and accompanying RIE method withchloride based etching gas, so as to form a pattern of the piezoelectriclayer 15. The AlN film is delineated such that one of the sidewall facesof the piezoelectric layer 15 may be located on the metallicintermediate electrode 13, and part of the metallic intermediateelectrode 13 comes to show up from the contour of the piezoelectriclayer 15. Further, in the plan view of FIG. 1, the branch member ofstriped configuration which is established at one of the sides of therectangular pattern of the sacrificial layer 21, comes to show up fromthe contour of the piezoelectric layer 15. The AlN film may beselectively etched by RIE method with chloride based etching gas, in acase using a Mo film for the metallic intermediate electrode 13, whichserves indirectly as an etching stopper layer over the bottom electrode14. If the metallic intermediate electrode 13 is formed of suchelectrically-conductive materials as W, Mo, Ru, Rh, Pd, Ir and Pt, otherthan Ir, the etching selectivity of the piezoelectric dielectric film(mother material film) for the piezoelectric layer 15 over the metallicintermediate electrode 13 can be increased and the metallic intermediateelectrode 13 serves as the etching stopper layer when the piezoelectriclayer 15 is delineated.

(d) Subsequently, an Al film having a 150 to 600 nm film thickness, orpreferably a 250 to 350 nm film thickness, is deposited so that the Alfilm can cover entire surfaces of the piezoelectric layer 15, themetallic intermediate electrode 13 laid bare from the contour of thepiezoelectric layer 15, and the insulting film 12. Afterwards the Alfilm is delineated by photolithography and accompanying wet etchingusing such solutions as potassium hydroxide (KOH), tetra methyl ammoniumhydroxide (TMAH), so as to form the top electrode 16 and the bottomelectrode wiring 17 as shown in FIG. 11D.

(e) Next, the branch member of striped configuration in the rectangularpattern of the sacrificial layer 21, being laid bare from the contour ofthe piezoelectric layer 15, is etched by submerging the substrate 11 inhydrogen peroxide (H₂O₂) solution, the temperature of which is set at 50degrees C. As etching of the branch member in the striped configurationproceeds, a conduit of the etching solution to the Mo sacrificial layer21, which is buried in the bottom surface (belly) of the piezoelectriclayer 15, is formed. And the Mo sacrificial layer 21 is etched throughthe conduit of the etching solution, so as to form the trapezoidalcavity 19 shown in FIG. 10. After the etching by using the H₂O₂solution, rinsed by isopropyl alcohol and dried, the cross-sectionalstructure shown in FIG. 11D is completed.

According to the manufacturing method of the FBAR of the secondembodiment, by establishing the metallic intermediate electrode 13formed of such materials as W, Mo, Ru, Rh, Pd, Ir, Pt, the etchingselectivity of the piezoelectric layer 15 over the bottom electrode 14can be ensured to some extent. In other words, the metallic intermediateelectrode 13 can serve as the etching stopper indirectly toward thebottom electrode 14 when the pattern of the piezoelectric layer 15 isdelineated. Therefore, there is no possibility that the bottom electrode14 becomes too thin by over-etching and is disconnected byafter-corrosion. And, because the metallic intermediate electrode 13 canprevent increase of the series resistance of the bottom electrode 14over a designated value by etching failure, an excellent high frequencycharacteristic in frequency band up to GHz can be achieved.

According to the manufacturing method of the FBAR of the secondembodiment, the metallic intermediate electrode 13 is so formed that themetallic intermediate electrode 13 is formed of electrically-conductivematerials which have the large etching selectivity over thepiezoelectric layer 15, any material constraints for the bottomelectrode 14 and process margins for the film thickness of the bottomelectrode 14 are not necessary. And, since the film thickness of themetallic intermediate electrode 13 has no relation with resonatorcharacteristics directly, it is possible to increase the film thicknessof the metallic intermediate electrode 13. Furthermore, a range ofselecting materials for the bottom electrode 13, in view of resistivityand etching selectivity, etc., can be expanded. Further a margin forinstabilities of processes such as fluctuation of the processingcondition also extends. Therefore, a large technical advantage in themanufacturing of the FBAR is achieved by the employment of the metallicintermediate electrode 13.

Note that before the process of depositing the Al film of FIG. 11B, itis preferable to deposit an amorphous metallic film formed of suchmaterials as a Ta—Al alloy film and a TiB₂ film having a 5 to 100 nmfilm thickness, or preferably a 15 to 30 nm film thickness, so that theamorphous metallic film may cover the entire surface of the sacrificiallayer 21. Namely, when the amorphous metallic film is deposited betweenthe bottom electrode 14 and the sacrificial layer 21, the c-axisorientation of the AlN film, which deposits on the amorphous metallicfilm, is remarkably improved. Compared with a case in which theamorphous metallic film is not established, the electromechanicalcoupling factor k_(t) ² and the Q-value which affect greatlyperformances of the FBAR can increase when the amorphous metallic film37 is deposited. And as mentioned in the modification of the firstembodiment, high frequency characteristic is further improved byselectively etching the amorphous metallic film, which exposes at thebottom face of the cavity 18.

The FBARs according to the second embodiment can implement theladder-type filter 41 shown in FIG. 6 and the VCO of mobilecommunication devices shown in FIG. 7 as mentioned in the firstembodiment. Also the FBAR of the second embodiment can be employed inthe portable transceiver shown in FIG. 8 and FIG. 9, so as to implementthe micro mechanical filters for the RF filter 41 and the IF filter 42.

Third Embodiment

As shown in FIG. 12, a FBAR according to a third embodiment of thepresent invention includes a substrate 11, an insulating film 12 formedon the substrate 11, an intermediate electrode 23 located such that theintermediate electrode 23 penetrates through the insulating film 12 andis buried into the substrate 11 with a bathtub-shaped (reversetrapezoid) or a U-groove configuration, a bottom electrode 14 disposedon the insulating film 12 and on the intermediate electrode 23, apiezoelectric layer 15 disposed on the bottom electrode 14 and on theintermediate electrode 23, a top electrode 16 delineated on thepiezoelectric layer 15 and a bottom electrode wiring 17 connected to theintermediate electrode 23. FIG. 12 shows a cross-sectional view of theFBAR of the third embodiment. Since a planar pattern of the FBAR issimilar to FIG. 1A, the illustration is omitted, the piezoelectric layer15 covers the entire surface of the bottom electrode 14 in the inside ofthe area defined by the contour of the piezoelectric layer 15 in a planview. And similar to the plan view shown in FIG. 1A, the contour of thepiezoelectric layer 15 crosses a top surface of the intermediateelectrode 23 and part of the intermediate electrode 23 extends to anoutside of the contour of the piezoelectric layer 15, from a contour ofthe piezoelectric layer 15.

A planar shape of the intermediate electrode 23 is a rectangle in astriped configuration similar to FIG. 1A. One side of the bottomelectrode 14 is disposed on the metallic intermediate electrode 13 andthe bottom electrode 14 and the intermediate electrode 23 areelectrically connected. In addition, the FBAR according to the thirdembodiment includes a cavity 18, which is formed along a direction fromthe bottom surface of the substrate 11 to the top surface of thesubstrate 11 for exposing a bottom surface of the bottom electrode 14.Therefore, part of the bottom electrode 14 is mechanically suspendedabove a cavity 18 and another part of which is mechanically fixed to thesubstrate 11. In the FBAR shown in FIG. 12, resonance frequency can bedetermined by adjusting the film thickness of the piezoelectric layer 15and the bottom electrode 14, since the FBAR utilizes a longitudinalvibration mode along the thickness direction of the piezoelectric layer15.

Similar to the FBARs of the first and second embodiments, since theintermediate electrode 23 of the FBAR according to the third embodimentmay have the bcc lattice structure of <110> orientation, the fcc latticestructure of <111> orientation, or alternatively the hcp latticestructure of <0001> orientation, by designating the orientation of theintermediate electrode 23 to be a specific orientation which facilitatesthe matching with <0001> orientation of hexagonal crystal having awurtzite lattice structure, the orientation of the piezoelectric layer15 is easy to be oriented uniformly along the c-axis, namely along theorientation <0001> orientation. Therefore, by controlling a polarizationdirection (orientation) of the piezoelectric layer 15 to the c-axis, ahigh electromechanical coupling factor k_(t) ² and a high Q-value areeasy to be ensured. Therefore, similar to the FBARs of the first andsecond embodiments, for material of the intermediate electrode 23 of theFBAR according to the third embodiment, a metallic film, which includesat least one of the metals selected from a group consisting of Ta, Mo,W, Ni, Co, Cr, Cu, Ti, Ir, Ru and Pt, is preferable. Other structure andmaterials are similar to the structure and materials already explainedin the first and second embodiments, and overlapping or redundantdescription may be omitted in the third embodiment.

And, different from the FBARs of the first and second embodiments, sincethe cross sectional shape of the intermediate electrode 23 of the FBARof the third embodiment has a bathtub-shaped (reverse trapezoid) or aU-groove configuration, reverse taper angles at both edges of theintermediate electrode 23 does not affect the orientation of thepiezoelectric layer 15. Therefore, each of the reverse taper angles maybe above 45 degrees. However, in respect of area efficiency, it is moresuitable to set the taper angle at the edge of the intermediateelectrode 23 to be 90 degrees, namely to delineate the intermediateelectrode 23 so as to be defined by a vertical sidewall so that theoccupation area by the intermediate electrode 23 is minimized. When thetaper angles at the edges of the metallic intermediate electrode 13 areset above 90 degrees, the occupation area by the intermediate electrode23 relatively increases and the area efficiency decreases, which doesnot meet the demand for miniaturization.

For instance, the FBAR encompassing the intermediate electrode 23 formedof W film with a 400 nm film thickness, the bottom electrode 14 formedof Al film with a 300 nm film thickness, the piezoelectric layer 15formed of AlN film with a 2.5 μm film thickness, the top electrode 16formed of Al film with a 300 nm film thickness and the bottom electrodewiring 17 formed of Al film with a 300 nm film thickness shows excellentresonance characteristics such that at a resonance frequency of 2.0 GHz,the electromechanical coupling factor k_(t) ² is 6.5%, the Q-value atthe resonance frequency is 800, and the Q-value at the anti-resonancefrequency is 680, according to an evaluation by a measurement using avector network analyzer.

With reference to FIGS. 13A-13E, a sequence of manufacturing processesof the FBAR according to the third embodiment is explained. Note thatthe FBAR of the third embodiment can be manufactured by variousmanufacturing methods including a modification of the third embodiment,other than the sequence of manufacturing processes disclosed by thefollowing example.

(a) First, as shown in FIG. 13A, on the Si (100) substrate 11 on whichan insulating film 12 is formed by thermal oxidation methods, etc., abathtub-shaped (shaped like the letter U) cavity having a 200 to 800 nmdepth, or preferably a 300 to 500 nm depth, is delineated by RIE methodwith fluoride based etching gas.

(b) For instance, when the bathtub-shaped cavity having a 400 nm depthis used, a W film, having a 600 nm film thickness, is deposited using RFmagnetron sputtering, etc. And the top surface of the W film isplanarized by chemical mechanical polishing (CMP) so as to bury anintermediate electrode 23 in the bathtub-shaped cavity. Next, on theinsulating film 12 and on the intermediate 23, an Al film, having a 150to 600 nm film thickness, or preferably a 250 to 350 nm film thickness,is deposited as a piezoelectric dielectric film (mother material film)using RF magnetron sputtering, etc. And the Al film is delineated byphotolithography and RIE method using chloride based etching gas, so asto form a bottom electrode 14 as shown in FIG. 13B. The Al film isdelineated such that the one side of the bottom electrode 14 is locatedon the intermediate electrode 23 and the bottom electrode 14 and theintermediate electrode 23 are electrically connected.

(c) Afterwards, as shown in FIG. 13C, on the bottom electrode 14 and onthe intermediate electrode 23, an AlN film, having a 2.5 μm filmthickness, is stacked using RF magnetron sputtering, etc. And the AlNfilm is delineated by photolithography and accompanying RIE method withchloride based etching gas, so as to form a pattern of the piezoelectriclayer 15. The AlN film is delineated such that one of the sidewall facesof the piezoelectric layer 15 may be located on the intermediateelectrode 23, and part of the intermediate electrode 23 comes to show upfrom the contour of the piezoelectric layer 15. The AlN film may beselectively etched by RIE method with chloride based etching gas, sincethe W film is used for the intermediate electrode 23, which servesindirectly as an etching stopper layer over the bottom electrode 14.

(d) Subsequently, an Al film having a 150 to 600 nm film thickness, orpreferably a 250 to 350 nm film thickness, is deposited so that the Alfilm can cover the entire surfaces of the piezoelectric layer 15, theintermediate electrode 23 laid bare from the contour of thepiezoelectric layer 15, and the insulting film 12. Afterwards the Alfilm is delineated by photolithography and accompanying wet etchingusing a combination of nitric acid (HNO₃), acetic acid (CH₃COOH),phosphoric acid (H₃PO₄) so as to delineate the top electrode 16 and thebottom electrode wiring 17 c as shown in FIG. 13D. The bottom electrodewiring 17 is electrically connected to the intermediate electrode 23laid bare from the contour of the piezoelectric layer 15.

(e) Next, after the thickness of the Si substrate 11 is adjusted to 100nm by polishing, an etching-mask is delineated on the bottom surface ofthe Si substrate 11 by photolithography using a lithography alignerconfigured to facilitate projection of images on both sides of the Sisubstrate 11. And the Si substrate 111 is selectively etched from thebottom surface by RIE method with CF₄ and SF₆ etching gas, so as toestablish the cavity 18 p as shown in FIG. 5E. Afterwards, the insultingfilm 12, which remains at the bottom of the cavity 18 p, is removed asshown in FIG. 12, using wet etching by RIE method with fluoride basedetching gas, thereby completing the sequence of formation processes ofthe FBAR of the third embodiment.

Note that before the process of depositing the Al film of FIG. 13B, itis preferable to deposit an amorphous metallic film formed of suchmaterials as a Ta—Al alloy film and a TiB₂ film having a 5 to 100 nmfilm thickness, or preferably a 15 to 30 nm film thickness, so that theamorphous metallic film may cover the entire surface of the insulatingfilm 12. Namely, when the amorphous metallic film is deposited betweenthe bottom electrode 14 and the insulating film 12, the c-axisorientation of the AlN film, which deposits on the amorphous metallicfilm, is remarkably improved. Compared with a case in which theamorphous metallic film is not established, the electromechanicalcoupling factor k_(t) ² and the Q-value which affect greatlyperformances of the FBAR can be increased when the amorphous metallicfilm 37 is deposited. And as mentioned in the first embodiment, highfrequency characteristic is further improved by selectively etching theamorphous metallic film, which exposes at the bottom face of the cavity18.

According to the manufacturing method of the FBAR of the thirdembodiment, although the intermediate electrode 23 is formed of such amaterial as W, the intermediate electrode 23 can also be formed of suchelectrically conductive materials as W, Mo, Ru, Rh, Pd, Ir and Pt. Byestablishing the intermediate electrode 23 formed of such materials asW, Mo, Ru, Rh, Pd, Ir, and Pt, the etching selectivity of thepiezoelectric layer 15 over the bottom electrode 14 can be ensured tosome extent. In other words, the intermediate electrode 23 can serve asthe etching stopper indirectly toward the bottom electrode 14 when thepattern of the piezoelectric layer 15 is delineated. Therefore, there isno possibility that the bottom electrode 14 becomes too thin byover-etching and is disconnected by after-corrosion. And, because theintermediate electrode 23 can prevent increase of the series resistanceof the bottom electrode 14 over a designated value by etching failure,an excellent high frequency characteristic in frequency band up to GHzcan be achieved.

According to the manufacturing method of the FBAR of the thirdembodiment, the intermediate electrode 23 is so formed that theintermediate electrode 23 is formed of electrically-conductive materialswhich have the large etching selectivity over the piezoelectric layer15, any material constraints for the bottom electrode 14 and processmargins for the film thickness of the bottom electrode 14 are notnecessary. And, since the film thickness of the intermediate electrode23 has no relation with resonator characteristics directly, it ispossible to increase the film thickness of the intermediate electrode23. Furthermore, a range of selecting materials for the bottom electrode23, in view of resistivity and etching selectivity, etc., can beexpanded. Further a margin for instabilities of processes such asfluctuation of the processing condition also extends. Therefore, a largetechnical advantage in the manufacturing of the FBAR is achieved by theemployment of the intermediate electrode 23.

The FBAR according to the third embodiment can implement the ladder-typefilter 41 shown in FIG. 6 and the VCO of mobile communication devicesshown in FIG. 7 as mentioned in the first embodiment. Also a pluralityof FBARs of the third embodiment can be employed in the portabletransceiver shown in FIG. 8 and FIG. 9, so as to implement the micromechanical filters for the RF filter 41 and the IF filter 42.

Fourth Embodiment

As shown in FIG. 14, a FBAR according to a fourth embodiment of thepresent invention includes a substrate 11, a cavity 20, having abathtub-shaped (reverse trapezoid) or a U-groove configuration, formedon the top surface of the 15 substrate 11, a bottom electrode 14, partof which is mechanically suspended above a cavity 20 and another part ofwhich is mechanically fixed to the substrate 11, the cavity 20 is formedbetween the substrate 11 and the bottom electrode 14, a metallicintermediate electrode 13 disposed on the top surface of the differentsite of the substrate 11 apart from the site in which the cavity 20 isformed, configured to be 20 electrically connected with the bottomelectrode 14, a piezoelectric layer 15 disposed on the bottom electrode14 and on the metallic intermediate electrode 13, a top electrode 16delineated on the piezoelectric layer 15 and a bottom electrode wiring17 connected to the metallic intermediate electrode 13. The cavity 20 isa closed cavity implemented by a groove dug at a top surface of and inthe substrate 11.

Since a planar pattern of the FBAR is similar to FIG. 1A, theillustration of the plan view is omitted, and FIG. 14 shows only across-sectional view of the FBAR of the fourth embodiment. Thepiezoelectric layer 15 covers the entire surface of the bottom electrode14 in the inside of the area defined by the contour of the piezoelectriclayer 15 in a plan view. And similar to the plan view shown in FIG. 1A,the contour of the piezoelectric layer 15 crosses a top surface of themetallic intermediate electrode 13 and part of the metallic intermediateelectrode 13 extends to an outside of the contour of the piezoelectriclayer 15, from the contour of the piezoelectric layer 15.

Similar to FIG. 1A, a shape of both sidewall faces in the edge of themetallic intermediate electrode 13 is a tapered configuration. And thetaper angle in the slanted sidewall of the metallic intermediateelectrode 13 may preferably set at below 45 degrees similar to the FBARof the first embodiment, and it is more preferable to set the taperangle at below 30 degrees and above ten degrees. A planar shape of themetallic intermediate electrode 13 is a striped configuration similar toFIG. 1A. One end of the bottom electrode 14 extends along a taperedsidewall face of the metallic intermediate electrode 13, and is disposedon the top surface of the metallic intermediate electrode 13. Andsimilar to the FBARs of the first to third embodiments, in the FBARshown in FIG. 14, resonance frequency can be determined by adjusting thefilm thicknesses of the piezoelectric layer 15 and the bottom electrode14, since the FBAR utilizes a longitudinal vibration mode along thethickness direction of the piezoelectric layer 15.

Also, similar to the FBARs of the first and third embodiments, since themetallic intermediate electrode 13 of the FBAR according to the fourthembodiment may have the bcc lattice structure of <110> orientation, thefcc lattice structure of <111 >orientation, or alternatively the hcplattice structure of <0001> orientation, the metallic intermediateelectrode 13 has a specific orientation which facilitates the matchingwith <0001> orientation of hexagonal crystal having a wurtzite latticestructure. Therefore, when AlN, or alternatively ZnO having the wurtzitelattice structure is employed to implement the piezoelectric layer 15,the orientation of the piezoelectric layer 15 is easy to be orienteduniformly along the c-axis, namely along the <0001> orientation. Bycontrolling a polarization direction (orientation) of the piezoelectriclayer 15 to the c-axis, an electromechanical coupling factor k_(t) ² anda Q-value are easy to be ensured. The features of the FBAR of the fourthembodiment is similar to the FBARs of the first to third embodiments,other overlapped explanations are omitted.

For instance, the FBAR of the fourth embodiment, encompassing themetallic intermediate electrode 13 formed of Mo film with a 400 nm filmthickness, the bottom electrode 14 formed of Al film with a 300 nm filmthickness, the piezoelectric layer 15 formed of AlN film with a 2.5 μmfilm thickness, the top electrode 16 formed of Al film with a 300 nmfilm thickness and the bottom electrode wiring 17 formed of Al film witha 300 nm film thickness shows excellent resonance characteristics suchthat at a resonance frequency of 2.1 GHz, the electromechanical couplingfactor k_(t) ² is 6.3%, the Q-value at the resonance frequency is 700,and the Q-value at the anti-resonance frequency is 580, according to anevaluation by a measurement using a vector network analyzer.

With reference to FIGS. 15A-15D, a sequence of manufacturing processesof the FBAR according to the fourth embodiment is explained. Note thatthe FBAR of the fourth embodiment can be manufactured by variousmanufacturing methods including various modifications of the fourthembodiment, other than the sequence of manufacturing processes disclosedby the following example.

(a) First, as shown in FIG. 15A, on the Si (100) substrate 11, a groove31 having a 0.5 to 2 μm depth, or preferably a 0.8 to 1.5 μm depth, byphotolithography with fluoride based etching gas, is formed. A plan viewof the groove 31 is a rectangular pattern in which a branch member ofstriped configuration is established so that the branch member ofstriped configuration is orthogonal to one of the sides of therectangular pattern, although the plan view is omitted. More than twobranch members may be established to the rectangular pattern.

(b) For instance, when the groove 31 has a 1.0 μm depth, a BPSG film,having an about 1.2 μm film thickness is deposited by chemical vapordeposition (CVD) method on the groove 31, and the BPSG film isplanarized by CMP method so as to form a pattern of a sacrificial layer32. A plan view of the sacrificial layer 32 is a similar rectangularpattern to the plan view of the groove 31, in which a branch member ofstriped configuration is established so that the branch member ofstriped configuration is orthogonal to one of the sides of therectangular pattern. Next, a Mo film, having a 200 to 700 nm filmthickness, or preferably a 300 to 500 nm film thickness, is deposited onthe substrate 11 and on the sacrificial layer 32 and is delineated byphotolithography and accompanying RIE method using chloride basedetching gas, so as to form a metallic intermediate electrode 13.Further, a Ru film, having a 150 to 600 nm, or preferably a 100 to 150nm film thickness, is stacked using RF magnetron sputtering, etc. Andthe Ru film is delineated by photolithography and accompanying RIEmethod with chloride based etching gas, so as to form a pattern of thebottom electrode 14 as shown in FIG. 15B. In the formation process, oneof the ends of the bottom electrode 14 is stacked on the metallicintermediate electrode 13 so that the bottom electrode 14 electricallyconnects to the metallic intermediate electrode 13.

(c) Afterwards, as shown in FIG. 15C, on the bottom electrode 14 and onthe metallic intermediate electrode 13, an AlN film, having an about 2.5μm film thickness, is stacked as a piezoelectric dielectric film (mothermaterial film) using RF magnetron sputtering, etc. And the AlN film isdelineated by photolithography and accompanying RIE method with chloridebased etching gas, so as to form a pattern of the piezoelectric layer 15as shown in FIG. 15C. The AlN film is delineated such that one of thesidewall faces of the piezoelectric layer 15 may be located on themetallic intermediate electrode 13, and part of the metallicintermediate electrode 13 comes to show up from the contour of thepiezoelectric layer 15. The AlN film may be selectively etched by RIEmethod with chloride based etching gas, if a Mo film is employed for themetallic intermediate electrode 13, because the Mo film servesindirectly as an etching stopper layer over the bottom electrode 14.Further, in the plan view of FIG. 15C, the branch member of stripedconfiguration which is established at one of the sides of therectangular pattern of the sacrificial layer 32, comes to show up fromthe contour of the piezoelectric layer 15.

(d) Subsequently, an Ru film having a 100 to 600 nm film thickness, orpreferably a 100 to 150 nm film thickness, is deposited so that the Rufilm can cover entire surfaces of the piezoelectric layer 15, themetallic intermediate electrode 13 laid bare from the contour of thepiezoelectric layer 15, and the substrate 11. Afterwards the Ru film isdelineated by photolithography and accompanying dry etching withchloride based etching gas, so as to form the top electrode 16 and thebottom electrode wiring 17 as shown in FIG. 15D. The bottom electrodewiring 17 is electrically connected to the metallic intermediateelectrode 13 laid bare from the contour of the piezoelectric layer 15.

(e) Next, the branch member of striped configuration in the rectangularpattern of the sacrificial layer 32, being laid bare from the contour ofthe piezoelectric layer 15, is etched by submerging the substrate 111 ina BPSG-etching solution such as fluoride acid (HF), fluoridationammonium (NH₄F). As etching of the branch member in the stripedconfiguration proceeds, a conduit of the etching solution to the Mosacrificial layer 32, which is buried in the bottom surface (belly) ofthe bottom electrode 14, is formed. And the Mo sacrificial layer 32 isetched through the conduit of the etching solution, so as to form thecavity 20 shown in FIG. 14. After the etching by the BPSG-etchingsolution, the substrate 11 is rinsed by isopropyl alcohol and dried, andthe cross-sectional structure shown in FIG. 15D is completed.

According to the manufacturing method of the FBAR of the fourthembodiment, although the metallic intermediate electrode 13 is formed ofa Mo film, the metallic intermediate electrode 13 can also be formed ofsuch electrically conductive materials as W, Ru, Rh, Pd, Ir and Pt. Byestablishing the semiconductor intermediate electrode 23 formed of suchmaterials as W, Mo, Ru, Rh, Pd, Ir, and Pt, the etching selectivity ofthe piezoelectric layer 15 over the bottom electrode 14 can be ensuredto some extent. In other words, the metallic intermediate electrode 13can serve as the etching stopper indirectly toward the bottom electrode14 when the pattern of the piezoelectric layer 15 is delineated.Therefore, there is no possibility that the bottom electrode 14 becomestoo thin by over-etching and is disconnected by after-corrosion. And,because the metallic intermediate electrode 13 can prevent increase ofthe series resistance of the bottom electrode 14 over a designated valueby etching failure, an excellent high frequency characteristic infrequency band up to GHz can be achieved.

According to the manufacturing method of the FBAR of the fourthembodiment, the metallic intermediate electrode 13 is so formed that themetallic intermediate electrode 13 is formed of electrically-conductivematerials which have a large etching selectivity over the piezoelectriclayer 15, any material constraints for the bottom electrode 14 andprocess margins for the film thickness of the bottom electrode 14 arenot necessary. And, since the film thickness of the metallicintermediate electrode 13 has no relation with resonator characteristicsdirectly, it is possible to increase the film thickness of the metallicintermediate electrode 13. Furthermore, a range of selecting materialsfor the bottom electrode 13, in view of resistivity and etchingselectivity, etc., can be expanded. Further a margin for instabilitiesof processes such as fluctuation of the processing conditions alsoextends. Therefore, a large technical advantage in the manufacturing ofthe FBAR is achieved by the employment of the metallic intermediateelectrode 13.

For a FBAR according to a modification of the forth embodiment, suchconfiguration is considered as to deposit an amorphous metallic filmunder the bottom electrode 14, similar to the modification of the firstembodiment shown in FIG. 3, in which the amorphous metallic film isdeposited between the bottom electrode 14 and the insulating film 12,and the c-axis orientation of the AlN film, which deposits on theamorphous metallic film, is remarkably improved. Compared with a case inwhich the amorphous metallic film is not established, theelectromechanical coupling factor k_(t) ² and the Q-value which affectgreatly performances of the FBAR can be increased when such amorphousmetallic film is deposited. Therefore, it is preferable to deposit anamorphous metallic film formed of such materials as a Ta—Al alloy filmand a TiB₂ film having a 5 to 100 nm film thickness, or preferably a 15to 30 nm film thickness, after the Mo film is deposited on the substrate11 and on the sacrificial layer 32 and the metallic intermediateelectrode 13 is delineated as shown in a manufacturing process of FIG.15B.

The FBAR according to the fourth embodiment can implement theladder-type filter 41 shown in FIG. 6 and the VCO of mobilecommunication devices shown in FIG. 7 as mentioned in the firstembodiment. Also a plurality of FBARs of the fourth embodiment can beemployed in the portable transceiver shown in FIG. 8 and FIG. 9, so asto implement the micro mechanical filters for the RF filter 41 and theIF filter 42.

Fifth Embodiment

As shown in FIG. 16, a FBAR according to a fifth embodiment of thepresent invention includes a substrate 11 formed of semi-insulating orhigh-resistivity material, a bottom electrode 14, part of which ismechanically suspended above a cavity 18 p and another part of which ismechanically fixed to the substrate 11, a piezoelectric layer 15, havingthe same shape and the same size as the bottom electrode 14 in a planview of FIG. 16A, disposed on the bottom electrode 14, a top electrode16 on the piezoelectric layer 15, a semiconductor intermediate electrode33 buried at and in a top surface of the substrate 11, being located ata contour of the piezoelectric layer 15, defining the shape of thepiezoelectric layer 15 in the plan view, the semiconductor intermediateelectrode 33 having a lower resistivity than the semiconductor substrate11, configured to be connected to the bottom electrode 14, a bottomelectrode wiring 17 connected to the semiconductor intermediateelectrode 33. The FBAR according to the fifth embodiment utilizes alongitudinal vibration mode along a thickness direction of thepiezoelectric layer 15. The semiconductor intermediate electrode 33 is aburied semiconductor region from the top surface of the semiconductorsubstrate 11 into the inside of the semiconductor substrate 11.

Further, the FBAR according to the fifth embodiment of the presentinvention includes an inter-layer dielectric film 34 formed on thepiezoelectric layer 15, the semiconductor substrate 11 being laid barefrom the contour of the piezoelectric layer 15 and the semiconductorintermediate electrode (impurity-diffused region) 33. Through a firstcontact window 36 a formed in the inter-layer dielectric film 34, thetop electrode 16 is electrically connected to the piezoelectric layer 15and through a second contact window 36 b formed in the inter-layerdielectric film 34, the bottom electrode wiring 17 is electricallyconnected to the semiconductor intermediate electrode 33. For materialsof the inter-layer dielectric film 34, various dielectric films such asa silicon oxide film (SiO₂), a silicon nitride (Si₃N₄) film or acomposite film of the silicon oxide film (SiO₂) and the silicon nitride(Si₃N₄) film can be used.

As semiconductor substrate 11, for instance a p-type silicon substrate,a main surface of which is implemented by a (100) plane of about 600 Ωcmto 10 kΩcm (impurity concentration of about 2×10¹³ cm⁻³-1×10¹² cm⁻³) isusable. In a case using the p-type silicon substrate, a n-type diffusedregion of 0.85 Ωcm-0.095 Ωcm (impurity concentration of about 1×10²⁰cm⁻³-5×10¹⁸ cm⁻³) with a depth of about 300 nm to 7 μm, can be adoptedfor the semiconductor intermediate electrode (impurity-diffused region)33. On the contrary, a p-type diffused region of 1.2 Ωcm-0.02 Ωcm(impurity concentration of about 1×10²⁰ cm⁻³-5×10¹⁸ cm⁻³) with a depthof about 300 nm to 7 μm, may be buried on a n-type silicon substrate forthe semiconductor intermediate electrode (impurity-diffused region) 33.In other words, the semiconductor intermediate electrode(impurity-diffused region) 33 can be implemented by a heavily dopedsemiconductor region buried in the semiconductor substrate 11 of a firstconductivity type, the heavily doped semiconductor region having asecond conductivity type opposite to the first conductivity type.Although an explanation hereinafter is made using such that p-type isassigned as the first conductivity type and n-type is assigned as thesecond conductivity type, n-type can be assigned as the firstconductivity type and p-type can be assigned as the second conductivitytype for establishing the semiconductor intermediate electrode(impurity-diffused region) 33. By burying the semiconductor intermediateelectrode 33 implemented by a semiconductor region of the secondconductivity type buried in a semiconductor substrate 11 of the firstconductivity type, a junction-isolation is established by pn junctionslocated in a space between adjacent semiconductor intermediateelectrodes 33, in an identical semiconductor substrate 11 on which aplurality of FBARs are monolithically integrated.

As shown in FIG. 16, the contour of the piezoelectric layer 15, definingthe shape of the piezoelectric layer 15, crosses a top surface of thesemiconductor intermediate electrode (impurity-diffused region) 33 andpart of the semiconductor intermediate electrode (impurity-diffusedregion) 33 extends to an outside of the contour of the piezoelectriclayer 15, from the contour of the piezoelectric layer 15.

A planar shape of the semiconductor intermediate electrode(impurity-diffused region) 33 is a rectangle in a striped configurationsimilar to FIG. 16. One side of the bottom electrode 14 is disposed onthe semiconductor intermediate electrode (impurity-diffused region) 33and the bottom electrode 14 and the semiconductor intermediate electrode(impurity-diffused region) 33 are electrically connected. In addition,the FBAR according to the fifth embodiment includes a cavity 18 p, whichis a open cavity formed along a direction from the bottom surface of thesubstrate 11 to the top surface of the substrate 11 for exposing abottom surface of the bottom electrode 14. Therefore, part of the bottomelectrode 14 is mechanically suspended above the cavity 18 p and anotherpart of which is mechanically fixed to the substrate 11. In the FBARshown in FIG. 16, resonance frequency can be determined by adjusting thefilm thicknesses of the piezoelectric layer 15 and the bottom electrode14, since the FBAR utilizes a longitudinal vibration mode along thethickness direction of the piezoelectric layer 15.

For instance, the FBAR of the fifth embodiment, encompassing thesemiconductor intermediate electrode (impurity-diffused region) 33formed of W film with a 400 nm film thickness, the bottom electrode 14formed of Al film with a 300 nm film thickness, the piezoelectric layer15 formed of AlN film with a 2.5 μm film thickness, the top electrode 16formed of Al film with a 300 nm film thickness and the bottom electrodewiring 17 formed of Al film with a 300 nm film thickness shows excellentresonance characteristics such that at a resonance frequency of 2.0 GHz,the electromechanical coupling factor k_(t) ² is 6.5%, the Q-value atthe resonance frequency is 800, and the Q-value at the anti-resonancefrequency is 680, according to an evaluation by a measurement using avector network analyzer.

With reference to FIGS. 17A-17D, a sequence of manufacturing processesof the FBAR according to the fifth embodiment is explained. Note thatthe FBAR of the fifth embodiment can be manufactured by variousmanufacturing methods including a modification of the fourth embodiment,other than the sequence of manufacturing processes disclosed by thefollowing example.

(a) First, a photoresist 35 is coated on the entire top surface of asemiconductor substrate 11, or a p-type Si (100) substrate 11 having ahigh-resistivity and the photoresist 35 is delineated by normalphotolithography technique so as to form a photoresist-mask. Through thephotoresist-mask, n-type impurity ions such as phosphorus ions (³¹P⁺)are implanted into the semiconductor substrate 11 with an accelerationvoltage of 80-150 kV, and a dose amount of about 3×10¹⁵ cm⁻²-4×10¹⁶ cm⁻²so as to form an ion implanted region 33i in the semiconductor substrate11 as shown in FIG. 17A. In a case in which dose amount is heavy, ametallic thin film such as an aluminum (Al) film may be delineated bythe photolithography technology for an ion-implantation mask, instead ofthe photoresist 35.

(b) And after the photoresist-mask used as the ion-implantation mask isremoved, the semiconductor substrate 11 is annealed in nitrogen (N₂) gasambient which contains 1-5% oxygen (O₂) gas or alternatively, in aninert gas such as helium (He), at 1100 degrees C. to 1200 degrees C. forabout 30 minutes to 2 hours. The process activates the implantedimpurity ions so as to form the semiconductor intermediate electrode(impurity-diffused region) 33 implemented by the n-typeimpurity-diffused region. Afterwards, a thin oxide film formed by theactivation annealing on the top surface of the semiconductor substrate11 is removed by diluted fluoride acid (HF) aqueous solution. Inaddition, an Al film (metallic film for the bottom electrode) 14 with a150 to 600 nm film thickness and 250 to 350 nm is formed on thesemiconductor substrate 11 and on the semiconductor intermediateelectrode (impurity-diffused region) 33 by using RF magnetron sputteringas shown in FIG. 17B. Afterwards, for instance, an AlN film 15 with a2.5 μm film thickness is deposited on the Al film 14 as shown in FIG.17C as “a piezoelectric dielectric film (mother material film) forforming the piezoelectric layer”.

(c) Next, after a new photoresist is coated on the entire top surface ofthe AlN film (piezoelectric dielectric film for forming thepiezoelectric layer) 15, the new photoresist on the AlN film isdelineated by photolithography. And by using the new photoresist as anetching mask, the AlN film (piezoelectric dielectric film for formingthe piezoelectric layer) 15 is selectively removed by RIE method withchloride based etching gas, so as to form a pattern of the piezoelectriclayer 15. Subsequently, in the same etching-chamber in which the patternof the piezoelectric layer 15 is delineated, the Al film (metallic filmfor the bottom electrode) 14 is selectively removed by RIE method withchloride based etching gas, so as to form a pattern of the bottomelectrode 14 as shown in FIG. 17D such that the pattern of the bottomelectrode 14 can have the same planar shape and the same size as thepattern of the piezoelectric layer 15, that part of the semiconductorsubstrate 11 and part of the semiconductor intermediate electrode(impurity-diffused region) 33 are exposed. In the process, as shown inFIG. 17D, one of the sidewall faces of the bottom electrode 14 may belocated on the semiconductor intermediate electrode (impurity-diffusedregion) 33, and the bottom electrode 14 and the semiconductorintermediate electrode (impurity-diffused region) 33 are electricallyconnected. Therefore, the pattern of the AlN film is simultaneouslydelineated with the same planar shape of the bottom electrode 14 suchthat, in a plan view, one of the sidewall faces of the piezoelectriclayer 15 may be located on the semiconductor intermediate electrode(impurity-diffused region) 33, and part of the semiconductorintermediate electrode (impurity-diffused region) 33 comes to show upfrom the contour of the piezoelectric layer 15.

(d) Further, on the piezoelectric layer 15 and on the semiconductorsubstrate 11, the semiconductor intermediate electrode(impurity-diffused region) 33 which come to show up from thepiezoelectric layer 15, an oxide film (a SiO₂ film) with a 100 nm to 800nm film thickness is deposited so as to form the inter-layer dielectricfilm 34 by CVD method. The inter-layer dielectric film 34 may be formedof a composite film between the silicon oxide film (SiO₂) and thesilicon nitride (Si₃N₄) film. Next, a new photoresist is coated on theinter-layer dielectric film 34, and the new photoresist is exposed withlight transmitted through a particular photo-mask by photolithographyand the new photoresist is developed so as to form an etching mask ofthe new photoresist. And by using the new photoresist as an etchingmask, the inter-layer dielectric film 34 is selectively removed by RIEmethod as shown in FIG. 17D, so as to open a pattern of the firstcontact window 36 a, making visible part of the piezoelectric layer 15,and to open a pattern of the second contact window 36 b, making visiblepart of the semiconductor intermediate electrode (impurity-diffusedregion) 33.

(e) Subsequently, an Al film having a 150 to 600 nm film thickness, orpreferably a 250 to 350 nm film thickness, is deposited on theinter-layer dielectric film 34 through the first contact window 36 a andthe second contact window 36 b. Afterwards, the Al film is delineated byphotolithography and accompanying wet etching using a combination ofnitric acid (HNO₃), acetic acid (CH₃COOH), phosphoric acid (H₃PO₄) so asto delineate the top electrode 16 and the bottom electrode wiring 17.The top electrode 16 is electrically connected to the top surface of thepiezoelectric layer 15 laid bare from the bottom surface of the firstcontact window 36 a and the bottom electrode wiring 17 is electricallyconnected to the semiconductor intermediate electrode (impurity-diffusedregion) 33 laid bare from the bottom surface of the second contactwindow 36 b respectively.

(f) Next, after the thickness of the semiconductor substrate 11 isadjusted to 100 nm by polishing, an etching-mask is delineated on thebottom surface of the semiconductor substrate 11 by photolithographyusing a photolithography aligner configured to project images on bothsides of the semiconductor substrate 11. And the semiconductor substrate11 formed of silicon, is selectively etched from the bottom surface byRIE method with CF₄ and SF₆ etching gas, so as to establish the cavity18 p as shown in FIG. 16.

Note that in the above-mentioned description, though a case in which thesemiconductor intermediate electrode (impurity-diffused region) 33 isformed through ion implantation, various diffusion methods such as vaporphase diffusion (pre-deposition) using liquid diffusion-sources such asphosphoryl chloride (POCl₃) and vapor diffusion-sources such asphosphine (PH₃) gas, etc., solid phase diffusion using phosphosilicateglass (PSG), can be adopted for establishing the semiconductorintermediate electrode (impurity-diffused region) 33 And in the vaporphase diffusion, an silicon oxide film having an about 600 nm to 1 μmfilm thickness may be used as a diffusion mask.

Generally, a FBAR has a simple configuration such that a piezoelectriclayer 15 is sandwiched by a bottom electrode 14 and a top electrode 16.Because a film thickness of the piezoelectric layer 15 is usually above1 μm, the general FBAR is accompanied by various technical problems.Namely, the piezoelectric layer 15 is susceptible to be cracked by astress ascribable to a level difference in the boundary where the bottomelectrode 14 is inserted under the piezoelectric layer 15. Thepiezoelectric layer 15 is subject to be cracked because the filmthickness becomes thick when we attempt to reduce the stress inpiezoelectric layer 15,and because the piezoelectric layer 15 has agrain crystal structure in a pillar configuration. Therefore in anearlier technology, it is necessary that the bottom electrode 14 isdelineated so as to be associated with taper angles, which are set atseveral decades degree. However, the controlling of the taper angle isactually very difficult. Even though the taper angles are implemented bysidewalls of the bottom electrode 14, by residual stresses in thepiezoelectric layer 15 concentrate around locations at which the taperedsidewalls of the piezoelectric layer 15 begin, and to locations at whichthe tapered sidewall end above the bottom electrode 14, there is a highpossibility that cracks would occur around the location at which thetapered sidewall begins and around the locations at which the taperedsidewall end, which reduces a manufacturing yield to a low level.

However, according to the manufacturing method of the FBAR of the fifthembodiment, the semiconductor intermediate electrode (impurity-diffusedregion) 33 can be formed without a level difference on part of thesemiconductor substrate 11, and a piezoelectric film is stacked on thebottom electrode 14 successively so that piezoelectric layer 15 isdelineated simultaneously with the bottom electrode 14 as a single pieceof unit. Because the simultaneous delineation process is employed, thereis no level difference of the piezoelectric layer 15 on the bottomelectrode 14, and there is no sidewall defined by the taper angle.Therefore, the generation of the cracks in the piezoelectric layer 15can be prevented, and it is not necessary that the taper angel of thebottom electrode 14 is strictly controlled at several decades degreesand the manufacturing yield becomes high.

Also a characteristic of the piezoelectric layer 15 has a close relationwith the orientation of a film of the piezoelectric layer 15. So as toobtain a highly-oriented film along the c-axis, it is preferable thatthe piezoelectric layer 15 is successively disposed on a highly-orientedbottom electrode 14. According to the manufacturing method of the FBARof the fifth embodiment, the piezoelectric layer 15, which is stacked onthe bottom electrode 14, is delineated simultaneously with the bottomelectrode 14 as a single piece of unit, and the highly orientedpiezoelectric layer 15 can be grown. In the result, theelectromechanical coupling factor k_(t) ² and the Q-value can beincreased.

According to the manufacturing method of the FBAR of the fifthembodiment, there is no possibility that the bottom electrode 14 becomestoo thin by over-etching and is disconnected by after-corrosion. And,because the semiconductor intermediate electrode (impurity-diffusedregion) 13 can prevent increase of the series resistance of the bottomelectrode 14 over a designated value by etching failure, an excellenthigh frequency characteristic in frequency band up to GHz can beachieved. Further, by the manufacturing method of the FBAR of the fifthembodiment, there is no necessity of cleaning processes of the topsurface of the bottom electrode 14 before the deposition of thepiezoelectric layer 15, and with a high-manufacturing yield, the FBARoperating with high efficiency can be manufactured at a low-cost.

First Modification of the Fifth Embodiment

A plan view of the semiconductor intermediate electrode(impurity-diffused region) 33 is not limited to the rectangle in thestriped shape as shown in FIG. 16. As shown in FIG. 18, in the FBAR of amodification (a first modification) of the fifth embodiment, a plan viewof the semiconductor intermediate electrode (impurity-diffused region)33 is a concave polygon, arranged like the letter C, disposed around thepiezoelectric layer 15. As similar to FIG. 16, since the bottomelectrode 14 is delineated so as to have the same planar shape and thesame size as the piezoelectric layer 15, the outer three sides of thebottom electrode 14, in a plan view, is located on the semiconductorintermediate electrode (impurity-diffused region) 33 in the inside ofthe occupied area defining the concave shape of the semiconductorintermediate electrode (impurity-diffused region) 33. Because the bottomelectrode 14 and the semiconductor intermediate electrode(impurity-diffused region) 33 are mutually electrically connected in theinner three sides of the concave polygon, arranged like the letter Cimplemented by the semiconductor intermediate electrode(impurity-diffused region) 33, the FBAR of the first modification of thefifth embodiment achieves a structure which can establish electricallylower resistance than the structure shown in FIG. 16.

The inter-layer dielectric film 34 is formed on the piezoelectric layer15, the semiconductor substrate 11 being laid bare from the sides of thepiezoelectric layer 15 and the semiconductor intermediate electrode(impurity-diffused region) 33. The semiconductor intermediate electrode(impurity-diffused region) 33 implemented by the concave polygon iselectrically connected to the bottom electrode wiring 17 through thesecond contact window 36 b formed in the inter-layer dielectric film 34.As shown in FIG. 18, by leaving a metallic film, etc, implemented by thebottom electrode wiring 17, even when the resistivity in thesemiconductor region (impurity diffused region) of the intermediateelectrode 33 is not low enough, resistance of the semiconductorintermediate electrode (impurity-diffused region) 33 can be decreasedeffectively by the metallic film, etc.

Further, through the first contact window 36 a formed in the inter-layerdielectric film 34, the piezoelectric layer 15 is electrically connectedto the top electrode 16 on the piezoelectric layer 15. The top electrode16 shown in the plan view of FIG. 18A extends vertically, different fromthe horizontal pattern of the top electrode 16 shown in the plan view ofFIG. 16. Other structure and materials are similar to the structure andmaterials of the FBAR already explained along FIG. 16, and overlappingor redundant description may be omitted in the fifth embodiment.

The plan view of the semiconductor intermediate electrode(impurity-diffused region) 33 is not limited to the concave polygon,arranged like the letter C, shown in FIG. 18, such a concave polygonarranged like the letter like the letter L formed along two adjacentsides of the bottom electrode 14, a rectangular loop configuration whichcircles along all sides of the bottom electrode 14, may be adopted, oralternatively, a rectangular area of striped shape may be arranged inparallel along two opposing sides of the bottom electrode 14.

[Micro Mechanical Filter]

The FBAR according to the fifth embodiment can implement the ladder-typefilter 41 shown in FIG. 6 and the VCO of mobile communication devicesshown in FIG. 7 as mentioned in the first embodiment. Also a pluralityof FBARs of the fifth embodiment can be employed in the portabletransceiver shown in FIG. 8 and FIG. 9, so as to implement the micromechanical filters for the RF filter 41 and the IF filter 42.Furthermore, the other example of a micro mechanical filter implementedby a plurality of FBARs of the fifth embodiment is shown with referenceto FIG. 19.

A ladder-type filter 41 shown in FIG. 19A is arranged so that sevenFBARs F_(a), F_(b), F_(c), F_(d), F_(e), F_(f), F_(g) are connected inseries and in parallel to each other. The FBARs F_(b), F_(d), F_(f) areconnected in series and the FBARs F_(a), F_(c), F_(e), F_(g) areconnected in parallel so as to implement the ladder-type filter 41 withthree and a half stages.

With regard to a circuit configuration of the ladder-type filter 41shown in FIG. 19A, when the ladder-type filter 41 is actuallymanufactured, various topologies can be considered. FIG. 19B is acircuit configuration equivalent to FIG. 19A, corresponding to a planview of FIG. 20 which shows an example in which the ladder-type filter41 is actually manufactured. FIG. 19B includes two common terminals202-1 and 202-2 at an input port P_(in) which are divided from aterminal 202 in FIG. 19A, and also FIG. 19B includes two commonterminals 204-1 and 204-2 at an output port P_(out) which are dividedfrom a terminal 204 in FIG. 19A

In FIG. 20, one of the terminals at input port P_(in), or theinput-terminal 201 is delineated as a common top electrode for the FBARsF_(a), F_(b). In other words, one of the terminals at input port P_(in),or the input-terminal 201 serves as a top electrode of the FBAR F_(a),and the other terminals at input port P_(in), or a common-terminal 201-1serves as a bottom electrode of the FBAR F_(a). In the FBAR F_(a) ofFIG. 20, a plan view of an semiconductor intermediate electrode(impurity-diffused region) 33 a is a rectangular loop shape whichcircles along all sides of a bottom electrode 210 and the semiconductorintermediate electrode (impurity-diffused region) 33 a is formed of an-type heavily doped region, buried in a p-type semiconductor substrate.And similar to FIGS. 16 and 18, the bottom electrode 210 is delineatedwith the same planar shape and the same size as the pattern of the FBARF_(a). Four sides of the bottom electrode 210 are located on inner sidesof the semiconductor intermediate electrode (impurity-diffused region)33 a rectangular loop shape. The bottom electrode 210 and thesemiconductor intermediate electrode (impurity-diffused region) 33 a areelectrically connected at a contact area assigned near the four sides ofthe semiconductor intermediate electrode (impurity-diffused region) 33a, the contact area is located in the semiconductor intermediateelectrode 33 a. Further, the semiconductor intermediate electrode(impurity-diffused region) 33 a of the rectangular loop is electricallyconnected to a bottom electrode wiring 202-1 through the second contactwindow 36 b formed in the inter-layer dielectric film 34. Two contactwindows 36 bs shown in FIG. 20A are arranged being shaped like theletter L along two adjacent sides of the bottom electrode 210. Andfurther, through the first contact window 36 a formed in the inter-layerdielectric film 34, the top electrode 201 shared with the FBAR F_(b), iselectrically connected to the FBAR F_(a).

As shown in FIG. 20, a pattern of the bottom electrode 211 of the FBARF_(b) is delineated so that the bottom electrode 211 can serve as abottom electrode shared between the FBAR F_(c) and the FBAR F_(d). Andsimilar to FIGS. 16 and 18, the common bottom electrode 211 for theFBARs F_(b), F_(c) and F_(d), is delineated with the same planar shapeand the same size as the pattern of the piezoelectric layers of theFBARs F_(b) F_(c), and F_(d) so as to delineate a single pattern of thepiezoelectric layers of the FBARs F_(b), F_(c) and F_(d).

And through the first contact window 36 a in the inter-layer dielectricfilm 34, the common top electrode 212 for the FBARs F_(d), the F_(f),and F_(g) is electrically connected to corresponding piezoelectriclayers of the FBARs F_(d), F_(f) and F_(g) respectively. A pattern of abottom electrode 213 of the FBAR F_(f) is delineated as a common bottomelectrode of the FBAR F_(e). The bottom electrode 213 is delineated withthe same planar shape and the same size as the patterns of thepiezoelectric layers of the FBARs F_(f) and F_(e), so as to delineate asingle pattern of the piezoelectric layers for the FBARs F_(f) andF_(e).

In the FBAR F_(f) of FIG. 20, a plan view of a semiconductorintermediate electrode (impurity-diffused region) 33f is a rectangularloop shape, which encloses around the first contact window 36 a of theFBAR F_(f). And the semiconductor intermediate electrode(impurity-diffused region) 33 f is an n-type heavily doped region,buried in a p-type semiconductor substrate. And, the semiconductorintermediate electrode (impurity-diffused region) 33 f of therectangular loop is electrically connected to a bottom electrode wiring203 through the two second contact windows 36 b in the inter-layerdielectric film 34. The bottom electrode wiring 203 is an out-putterminal at the output port P_(out) shown in FIG. 19. The two contactwindows 36 bs are arranged being shaped like the letter L along twoadjacent sides of the first contact window 36 a of the FBAR F_(f).

In the FBAR F_(g) of FIG. 20, a plan view of a semiconductorintermediate electrode (impurity-diffused region) 33 g is a rectangularloop shape which encloses around the first contact window 36 a of theFBAR F_(g). And the semiconductor intermediate electrode(impurity-diffused region) 33 g is an n-type heavily doped region,buried in the p-type semiconductor substrate. And, the semiconductorintermediate electrode (impurity-diffused region) 33 f and thesemiconductor intermediate electrode (impurity-diffused region) 33 g aremutually junction-isolated by pn-junctions between the p-typesemiconductor substrate and the n-type impurity-diffused regions, whichimplement the semiconductor intermediate electrode (impurity-diffusedregion) 33 f and the semiconductor intermediate electrode(impurity-diffused region) 33 g. And the semiconductor intermediateelectrode (impurity-diffused region) 33 g of the rectangular loop iselectrically connected to a bottom electrode wiring 204-2 through thesecond contact windows 36 b in the inter-layer dielectric film 34. Thebottom electrode wiring 204-2 is a common terminal at the output portP_(out) shown in FIG. 19B. The two contact windows 36 b are arrangedbeing shaped like the letter L along two adjacent sides of the firstcontact window 36 a of the FBAR F_(g).

Further, through each of the first contact windows 36 a in theinter-layer dielectric film 34, a piezoelectric layer of the FBAR F_(e)is electrically connected a top electrode 204-1 of the FBAR F_(e). Thetop electrode wiring 204-1 is a common terminal at the output portP_(out) shown in FIG. 19B.

Second Modification of the Fifth Embodiment

As shown in FIG. 21, a FBAR according to another modification (secondmodification) of the fifth embodiment of the present invention includesa substrate 11 formed of semi-insulating or high-resistivity material, asemiconductor intermediate electrode (impurity-diffused region) 33buried at and in a top surface of the substrate 11, an insulating film36 formed on the semiconductor intermediate electrode (impurity-diffusedregion) 33 and the substrate 11, a bottom electrode 14 formed on theinsulating film 36, a piezoelectric layer 15, having the same shape andthe same size as the bottom electrode 14 disposed on the bottomelectrode 14, an inter-layer dielectric film 34 formed on thepiezoelectric layer 15, an inter-layer dielectric film 34 formed on thepiezoelectric layer 15, the semiconductor substrate 11 being laid barefrom the sides of the piezoelectric layer 15 and the semiconductorintermediate electrode (impurity-diffused region) 33, a top electrode 16connected to the piezoelectric layer 15, through a contact window in theinter-layer dielectric film 34, and a bottom electrode wiring 17connected to the semiconductor intermediate electrode (impurity-diffusedregion) 33 through a contact window in the inter-layer dielectric film34. For materials of the insulating film 36, similar to the materialsfor the inter-layer dielectric film 34, various dielectric films such asa silicon oxide film (SiO₂), a silicon nitride (Si₃N₄) film or acomposite film of the silicon oxide film (SiO₂) and the silicon nitride(Si₃N₄) film can be used.

A plan view of the semiconductor intermediate electrode(impurity-diffused region) 33 is similar to the plan view shown in FIG.18, being shaped like the letter C, disposed around the piezoelectriclayer 15. Namely, the bottom electrode 14 is delineated having the sameplanar shape and the same size as the piezoelectric layer 15, threesides of the bottom electrode 14, in a plan view, are located on thesemiconductor intermediate electrode (impurity-diffused region) 33.However, the bottom electrode 14 and the semiconductor intermediateelectrode (impurity-diffused region) 33 are not materially connected,but are capacitively coupled, since the three sides of the semiconductorintermediate electrode (impurity-diffused region) 33 are formed throughthe insulating film 36. In a frequency bond having a resonance frequencyof 2.0 GHz, the bottom electrode 14 can be electrically connected to thesemiconductor intermediate electrode (impurity-diffused region) 33 eventhough such a capacitive coupling through the insulating film 36 isadopted.

As shown in FIG. 21, by protecting the semiconductor intermediateelectrode (impurity-diffused region) 33 with the insulating film 36, anoperation of the FBAR is further stabilized.

Other structure and materials are similar to the structure and materialsof the FBAR already explained along FIG. 18, and overlapping orredundant description may be omitted in the second modification of thefifth embodiment.

Sixth Embodiment

As shown in FIG. 22, a FBAR according to a sixth embodiment of thepresent invention includes a substrate 11 formed of semi-insulating orhigh-resistivity material, semiconductor intermediate electrodes(impurity-diffused regions) 33 buried at and in a top surface of thesubstrate 11, a cavity 20, having a bathtub-shaped (reverse trapezoid)or a U-groove configuration in a cross sectional view, formed at and inthe top surface of the substrate 11, sandwiched by the semiconductorintermediate electrodes (impurity-diffused regions) 33, a bottomelectrode 14, part of which is mechanically suspended above the cavity20 and another part of which is mechanically fixed to the substrate 11so that the cavity 20 is formed between the substrate 11 and the bottomelectrode 14, a piezoelectric layer 15, having the same shape and thesame size as the bottom electrode 14, disposed on the bottom electrode14, an inter-layer dielectric film 34 formed on the piezoelectric layer15, the semiconductor substrate 11 being laid bare from the contour ofthe piezoelectric layer 15 and the semiconductor intermediate electrode(impurity-diffused region) 33, a top electrode 16 connected to thepiezoelectric layer 15 through a contact window formed in theinter-layer dielectric film 34, a bottom electrode wiring 17 connectedto the semiconductor intermediate electrode 33 through a contact windowformed in the inter-layer dielectric film 34. The cavity 20 is a closedcavity implemented by a groove dug at a top surface of and in thesubstrate 11. For materials of the inter-layer dielectric film 34,various dielectric films such as a silicon oxide film (SiO₂), a siliconnitride (Si₃N₄) film or a composite film of the silicon oxide film(SiO₂) and the silicon nitride (Si₃N₄) film can be used, similar to theFBAR of the fifth embodiment. And as the semiconductor substrate 11, forinstance, a p-type silicon substrate, a main surface of which isidentified by a (100) plane, having a resistivity of about 600 Ωcm to 10k Ωcm (impurity concentration of about 2×10¹³ cm⁻³-1×10¹² cm⁻³), isusable. In a case using the p-type silicon substrate, a n-type diffusedregion of 0.001 Ωcm-0.02 Ωcm (impurity concentration of about 1×10²⁰cm⁻³-5×10¹⁸ cm⁻³) with a depth of about 300 nm to 7 μm, can be adoptedfor the semiconductor intermediate electrode (impurity-diffused region)33.

A plan view (not shown) of the semiconductor intermediate electrode(impurity-diffused region) 33 is concave polygon, similar to the planview shown in FIG. 18A, being shaped like the letter C, disposed aroundthe piezoelectric layer 15. Namely, the bottom electrode 14 isdelineated having the same planar shape and the same size as thepiezoelectric layer 15, three sides of the bottom electrode 14 arelocated on the semiconductor intermediate electrode (impurity-diffusedregion) 33 shaped in concave polygon. Through a second contact window 36b formed in the inter-layer dielectric film 34, the bottom electrodewiring 17 is electrically connected to the semiconductor intermediateelectrode (impurity-diffused region) 33 shaped in concave polygon. Asshown in FIGS. 18A and 18B, by leaving a metallic film, etc,implementing the bottom electrode wiring 17, on and around thesemiconductor intermediate electrode (impurity-diffused region) 33through the second contact window 36 b in the inter-layer dielectricfilm 34, even when the resistivity in the semiconductor region (impuritydiffused region) of the intermediate electrode 33 is not low enough,resistance of the semiconductor intermediate electrode(impurity-diffused region) 33 can be decreased effectively by themetallic film, etc. The plan view of the semiconductor intermediateelectrode (impurity-diffused region) 33 is not limited to the concavepolygon, arranged like the letter C, shown in FIG. 18A, another concavepolygon arranged like the letter L formed along two adjacent sides ofthe bottom electrode 14, a rectangular loop configuration which enclosesalong all sides of the bottom electrode 14, may be adopted, oralternatively, a rectangular area of striped shape may be arranged asshown in FIG. 16A. Further, in the FBAR of the sixth embodiment, throughthe first contact window 36 a formed in the inter-layer dielectric film34, the piezoelectric layer 15 is electrically connected to the topelectrode 16 on the piezoelectric layer 15. A plan view of the topelectrode 16 extends vertically, similar to the plan view of FIG. 18A.

With reference to FIGS. 23A-23E, a sequence of manufacturing processesof the FBAR according to the sixth embodiment is explained. Note thatthe FBAR of the sixth embodiment can be manufactured by variousmanufacturing methods including a modification of the sixth embodiment,other than the sequence of manufacturing processes disclosed by thefollowing example.

(a) First, as similar to FIG. 17A, a photoresist is coated on the entiretop surface of a semiconductor substrate 11, or a p-type Si (100)substrate 11 having a high-resistivity and the photoresist is delineatedby normal photolithography technique so as to form a photoresist-mask.Through the photoresist-mask, n-type impurity ions such as phosphorusions (³¹P⁺) are implanted into the semiconductor substrate 11 with anacceleration voltage of 80-150 kV, and a dose amount of about 3×10¹⁵cm⁻²-4×10¹⁶ cm⁻² so as to form an ion implanted region 33 in thesemiconductor substrate 11.

(b) And after the photoresist-mask used as the ion-implantation mask isremoved, the semiconductor substrate 11 is annealed in nitrogen (N₂) gasambient which contains 1-5% oxygen (O²) gas or alternatively, in aninert gas such as helium (He), at 1100-1200 degrees C. for about 30minutes to 2 hours. The process activates the implanted impurity ions soas to form the semiconductor intermediate electrode (impurity-diffusedregion) 33 implemented by the n-type impurity-diffused region.Afterwards, as shown in FIG. 23A, on the Si (100) substrate 11, a groove31 having a 0.5 to 2 μm depth, or preferably a 0.8 to 1.5 μm depth, isformed by photolithography with fluoride based etching gas. A plan viewof the groove 31 is a rectangular pattern in which a branch member ofstriped configuration is established so that the branch member ofstriped configuration is orthogonal to one of the sides of therectangular pattern, although the plan view is omitted. More than twobranch members may be established to the rectangular pattern.

(b) For instance, when the groove 31 has a 1.0 μm depth, a BPSG film,having an about 1.2 μm film thickness is deposited by chemical vapordeposition (CVD) method on the groove 31, and the BPSG film isplanarized by CMP method so as to form a pattern of a sacrificial layer32. A plan view of the sacrificial layer 32 is a similar rectangularpattern to the plan view of the groove 31, in which a branch member ofstriped configuration is established so that the branch member ofstriped configuration is orthogonal to one of the sides of therectangular pattern. Next, an Al film 14, or a metallic film for thebottom electrode, with a 150 to 600 nm film thickness, or preferably 250to 350 nm, is formed on the entire top surfaces of the semiconductorsubstrate 11 and the semiconductor intermediate electrode(impurity-diffused region) 33 by using RF magnetron sputtering as shownin FIG. 23B.

(c) Afterwards, for instance, an AlN film 15, or a piezoelectricdielectric film (mother material film) for forming the piezoelectriclayer, with a 2.5 μm film thickness is deposited on the entire topsurface of the Al film 14 as shown in FIG. 23C. And after a newphotoresist is coated on the entire top surface of the AlN film(piezoelectric dielectric film for forming the piezoelectric layer) 15,the new photoresist on the AlN film is delineated by photolithography.And by using the new photoresist as an etching mask, the AlN film(piezoelectric dielectric film for forming the piezoelectric layer) 15is selectively removed by RIE method with chloride based etching gas, soas to form a pattern of the piezoelectric layer 15. Subsequently, in thesame etching-chamber in which the pattern of the piezoelectric layer 15is delineated, the Al film (metallic film for the bottom electrode) 14is selectively removed by RIE method with chloride based etching gas, soas to form a pattern of the bottom electrode 14 as shown in FIG. 23Dsuch that the pattern of the bottom electrode 14 can have the sameplanar shape and the same size as the pattern of the piezoelectric layer15. In the process, as shown in FIG. 23D, part of the semiconductorsubstrate 11 and part of the semiconductor intermediate electrode(impurity-diffused region) 33 are laid bare. In other words, as shown inFIG. 23D, three sides of the bottom electrode 14 may be located on thesemiconductor intermediate electrode (impurity-diffused region) 33, andthe bottom electrode 14 and the semiconductor intermediate electrode(impurity-diffused region) 33 are electrically connected—although, in across-sectional view shown in FIG. 23D, as if two semiconductorintermediate electrodes (impurity-diffused regions) 33 appear under twosides of the bottom electrode 14, at the near side of the paper, thesemiconductor intermediate electrode (impurity-diffused region) 33 isalso formed under the other remaining side of the bottom electrode 14 soas to implement the concave polygon, shaped like the letter C. Further,in the plan view, a branch member of striped configuration, establishedin a rectangular pattern of the sacrificial layer 32, comes to show upfrom the side of a double-layer structure implemented by thepiezoelectric layer 15 and the bottom electrode 14.

(d) Further, on the piezoelectric layer 15, on the branch member of thesacrificial layer 32 and on the semiconductor substrate 11 and thesemiconductor intermediate electrode (impurity-diffused region) 33 whichcome to show up from the side of the piezoelectric layer 15, a siliconnitride (Si₃N₄) film with a 100 nm to 400 nm film thickness is depositedso as to form the inter-layer dielectric film 34 by CVD method. Theinter-layer dielectric film 34 may be formed of insulating materialswhich have a large etching selectivity over the BPSG film used for thepattern of the sacrificial layer 32, other than the silicon nitride(Si₃N₄) film. Next, a new photoresist is coated on the inter-layerdielectric film 34, and the new photoresist is exposed with lighttransmitted through a particular photo-mask by photolithography and thenew photoresist is developed so as to form an etching mask of the newphotoresist. And by using the new photoresist as an etching mask, theinter-layer dielectric film 34 is selectively removed by RIE method asshown in FIG. 23E, so as to open a pattern of the first contact window36 a, making visible part of the piezoelectric layer 15 and to open apattern of the second contact window 36 b, making visible part of thesemiconductor intermediate electrode (impurity-diffused region) 33.Although a cross-sectional view is omitted, in the process, theinter-layer dielectric film 34 formed on the branch member of thesacrificial layer 32 is selectively etched so as to form a conduit(longitudinal hole) of an etching solution.

(e) Next, the substrate 11 is submerged in a BPSG-etching solution suchas fluoride acid (HF), fluoridation ammonium NH₄F). By the process, thebranch member of striped configuration in a rectangular pattern of thesacrificial layer 32, laid bare from the side of the double-layerstructure of the piezoelectric layer 15 with the bottom electrode 14, isetched through the conduit (vertical hole) of the etching solution inthe inter-layer dielectric film 34. As etching of the branch member inthe striped configuration proceeds, a conduit (lateral hole) of theetching solution to the sacrificial layer 32, which is buried under thebottom surface (belly) of the bottom electrode 14, is formed. And thesacrificial layer 32 is etched through the conduit of the etchingsolution, so as to form the cavity 20 shown in FIG. 22. After theetching by the BPSG-etching solution, the substrate 11 is rinsed byisopropyl alcohol and dried.

(f) Subsequently, an Al film having a 150 to 600 nm film thickness, orpreferably a 250 to 350 nm film thickness, is deposited on theinter-layer dielectric film 34 through the first contact window 36 a andthe second contact window 36 b. Afterwards, the Al film is delineated byphotolithography and accompanying wet etching using a combination ofnitric acid (HNO₃), acetic acid (CH₃COOH), phosphoric acid (H₃PO₄) so asto delineate the top electrode 16 and the bottom electrode wiring 17.The top electrode 16 is electrically connected to the top surface of thepiezoelectric layer 15 laid bare from the bottom surface of the firstcontact window 36 a and the bottom electrode wiring 17 is electricallyconnected to the semiconductor intermediate electrode (impurity-diffusedregion) 33 laid bare from the bottom surface of the second contactwindow 36 b respectively.

The FBAR according to the sixth embodiment can implement the ladder-typefilter 41 shown in FIGS. 6 and 19, and the VCO of mobile communicationdevices shown in FIG. 7 as mentioned in the first embodiment. Also aplurality of FBARs of the sixth embodiment can be employed in theportable transceiver shown in FIG. 8 and FIG. 9, so as to implement themicro mechanical filters for the RF filter 41 and the IF filter 42.

Other Embodiments

Various modifications will become possible for those skilled in the artafter receiving the teaching of the present disclosure without departingfrom the scope thereof.

In the plan view of FIG. 20, the example of the configuration in whichthe micro mechanical filters implemented by a plurality of FBARsaccording to the fifth embodiment, are actually manufactured. Theladder-type filter 41 with three and a half stages shown in FIG. 19, isnot limited to such filters as implemented by the FBARs including thesemiconductor intermediate electrode (impurity-diffused region) 33. Forinstance, by adopting the FBAR having the intermediate electrode 23formed of metallic materials, the ladder-type filter 41 with three and ahalf stages shown in FIG. 19, can be achieved.

FIG. 24 shows an example in which the ladder-type filter 41 with threeand a half stages shown in FIG. 19, is implemented by using a pluralityof FBARs with such metallic intermediate electrode 23. In a plan view, apiezoelectric layer 15 is merged into a single piece of largerectangular pattern such that a piezoelectric layer 15 covers an entirearea which seven FBARs F_(a), F_(b), F_(c), F_(d), F_(e), F_(f), F_(g)occupy.

FIG. 25 shows a cross-sectional view of the FBAR F_(g) shown in FIG. 24,taken on line B-B. In the FBAR F_(g), a plan view of a metallicintermediate electrode 23 is a rectangle in a striped shape as shown ina broken line of FIG. 24, and the metallic intermediate electrode 23 gof rectangular shape is electrically connected to a bottom electrodewiring 204-2 through a contact window of rectangular slit formed in thepiezoelectric layer 15. The bottom electrode wiring 204-2 is a commonterminal at the output port P_(out) shown in FIG. 19B. The two contactwindows of rectangular slit are arranged as part of a pattern of themetallic intermediate electrode 23 g of the FBAR F_(g). In the FBARF_(g), one side of a bottom electrode 14 g is disposed on the metallicintermediate electrode 23 g and the bottom electrode 14 g and themetallic intermediate electrode 23 g are electrically connected. Inaddition, the FBAR F_(g) according to the other embodiment includes acavity 18, which is formed along a direction from a bottom surface of asubstrate 11 to a top surface of the substrate 11 for exposing a bottomsurface of the bottom electrode 14 g. Therefore, central part of thebottom electrode 14 g is mechanically suspended above the cavity 18 byfixing peripheral part of the bottom electrode 14 g to the substrate 11.

In FIG. 24, similar to FIG. 20, one of the terminals at input portP_(in), or the input-terminal 201 shown in FIG. 19, is delineated as acommon top electrode for the FBARs F_(a), F_(b). In other words, one ofthe terminals at input port P_(in), or the input-terminal 201 serves asa top electrode of the FBAR F_(a), and the other terminals at input portP_(in), or a common-terminal 202-1 serves as a bottom electrode of theFBAR F_(a). In FIG. 24, the FBAR F_(a) includes the metallicintermediate electrode 23 of rectangular shape shown in a broken line.

A plan view of the metallic intermediate electrode 23 of the FBAR F_(a)is a striped shape in a rectangular pattern as shown in the broken line.One side of the bottom electrode 14 a is located on one sides of themetallic intermediate electrode 23 of rectangular shape, the bottomelectrode 14 a and the metallic intermediate electrode 23 areelectrically connected in one side of the bottom electrode 14. Further,the metallic intermediate electrode 23 is electrically connected to abottom electrode wiring 202-1 through a contact window of rectangularslit formed in the piezoelectric layer 15 similar to the FBAR F_(g) (seeFIG. 25). The contact window of the rectangular slit is arranged alongone side of the bottom electrode 14.

As shown in FIG. 24, a pattern of a bottom electrode 211 of the FBARF_(b) is delineated so that the bottom electrode 211 can serve as acommon bottom electrode shared between the FBAR F_(c) and the FBARF_(d). Further, a common top electrode 212 for the FBARs F_(d), F_(f),and F_(g) is electrically connected to corresponding piezoelectriclayers 15 such that the common top electrode 212 is located opposing toeach of the corresponding bottom electrodes of the FBARs F_(d), F_(f),and F_(g) respectively.

A pattern of a bottom electrode 213 of the FBAR F_(f) is delineated as acommon bottom electrode of the FBAR F_(e). And a metallic intermediateelectrode 23 f of the FBAR F_(f) is electrically connected to a bottomelectrode wiring 203 through the contact window of the rectangular slitformed in the piezoelectric layer 15. The bottom electrode wiring 203 isan out-put terminal at the output port P_(out) shown in FIG. 19, whilethe FBAR F_(e) is electrically connected a top electrode 204-1. The topelectrode wiring 204-1 is a common terminal at the output port P_(out)shown in FIG. 19B.

FIG. 26 shows another example in which the ladder-type filter 41 withthree and a half stages shown in FIG. 19, is implemented by using aplurality of FBARs with a metallic intermediate electrode 13 shown inthe fifth embodiment. In a plan view, a piezoelectric layer 15 isarranged as a smaller rectangular pattern than the pattern ofpiezoelectric layer 15 shown in FIG. 24, such that a piezoelectric layer15 covers an area which seven bottom electrodes of seven FBARs F_(a),F_(b), F_(c), F_(d), F_(e), F_(f), F_(g) occupy. And the contour of thepiezoelectric layer 15, defining the shape of the piezoelectric layer15, crosses top surfaces of a metallic intermediate electrode 13 a ofthe FBAR F_(a), a metallic intermediate electrode 13 f of the FBARF_(f), a metallic intermediate electrode 13 g of the FBAR F_(g), shownin the broken line, respectively, parts of the metallic intermediateelectrodes 13 a, 13 f and 13 g extends to an outside of the contour ofthe piezoelectric layer 15, from the contour of the piezoelectric layer15

Plan views of the metallic intermediate electrodes 13 a, 13 f and 13 gare striped geometries in rectangular patterns as shown in the brokenline of FIG. 26.

FIG. 27 shows a cross-sectional view of the FBAR F_(g) shown in FIG. 26,taken on line B-B. In the FBAR F_(g), as shown in FIG. 27, sidewallfaces of the metallic intermediate electrodes 13 g is a taperedconfiguration. One side of a bottom electrode 14 g is connected on thetapered left sidewall face of the metallic intermediate electrodes 13 gand further extends on the metallic intermediate electrodes 13 g. Abottom electrode wiring 204-1 is electrically connected on the rightside of the metallic intermediate electrodes 13 laid bare from thesidewall face of the piezoelectric layer 15. A bottom electrode wiring204-2 is a common terminal at the output port P_(out) shown in FIG. 19B.Further a cavity 20, having a bathtub-shaped (reverse trapezoid) or aU-groove configuration is formed at and in a top surface of a substrate11, and part of a bottom electrode 14 g is mechanically suspended abovea cavity 20 and another part of which is mechanically fixed to thesubstrate 11.

In FIG. 26, similar to FIGS. 20 and 24, one of the terminals at inputport P_(in), or the input-terminal 201 shown in FIG. 19, is delineatedas a common top electrode for the FBARs F_(a), F_(b). In other words,one of the terminals at input port P_(in), or the input-terminal 201serves as a top electrode of the FBAR F_(a), and the other terminals atinput port P_(in), or a common-terminal 202-1 serves as a bottomelectrode wiring of the FBAR F_(a). In FIG. 26, the FBAR F_(a) includesa metallic intermediate electrode 13 a of rectangular shape shown in abroken line.

One side of a bottom electrode 14 a is located on inner sides of themetallic intermediate electrode 13 a of rectangular shape, the bottomelectrode 14 a and the metallic intermediate electrode 13 a areelectrically connected in one side of the bottom electrode 14. Further,the metallic intermediate electrode 13 a is electrically connected to abottom electrode wiring 202-1.

As shown in FIG. 26, a pattern of a bottom electrode 211 of the FBARF_(b) is delineated so that the bottom electrode 211 can serve as acommon bottom electrode shared between the FBAR F_(c), and the FBARF_(d). Further, a common top electrode 212 for the FBARs F_(d), F_(f),and F_(g) is electrically connected to corresponding piezoelectriclayers 15 such that the common top electrode 212 is located opposing toeach of the corresponding bottom electrodes of the FBARs F_(d), F_(f),and F_(g) respectively.

A pattern of a bottom electrode 213 of the FBAR F_(f) is delineated as acommon bottom electrode of the FBAR F_(e). And a metallic intermediateelectrode 13 f of the FBAR F_(f) laid bare from the sidewall face of thepiezoelectric layer 15 is electrically connected to a bottom electrodewiring 203. The bottom electrode wiring 203 is an out-put terminal atthe output port P_(out) shown in FIG. 19, while the FBAR F_(e) iselectrically connected a top electrode 204-1. The top electrode wiring204-1 is a common terminal at the output port P_(out) shown in FIG. 19B.

Thus, the present invention of course includes various embodiments andmodifications and the like which are not detailed above. Therefore, thescope of the present invention will be defined in the following claims.

1. A film bulk acoustic-wave resonator comprising: a substrate having acavity, the substrate being formed of one of semi-insulating materialand high-resistivity material; a bottom electrode partially fixed to thesubstrate, part of the bottom electrode is mechanically suspended abovethe cavity; a piezoelectric layer disposed on the bottom electrode, theshape of the piezoelectric layer is defined by a contour; a topelectrode on the piezoelectric layer; a semiconductor intermediateelectrode buried at and in a surface of the substrate, being located atthe contour of the piezoelectric layer, the semiconductor region havinga lower resistivity than the substrate, the intermediate electrode isconnected to the bottom electrode in the inside of the contour; and abottom electrode wiring connected to the semiconductor intermediateelectrode extending from the contour to an outside of the contour in theplan view, wherein a longitudinal vibration mode along a thicknessdirection of the piezoelectric layer is utilized.
 2. The film bulkacoustic-wave resonator of claim 1, further comprising: an inter-layerdielectric film formed on the piezoelectric layer, the semiconductorsubstrate being laid bare from the contour of the piezoelectric layerand the semiconductor intermediate electrode, wherein through a firstcontact window formed in the inter-layer dielectric film, the topelectrode is electrically connected to the piezoelectric layer andthrough a second contact window formed in the inter-layer dielectricfilm, the bottom electrode wiring is electrically connected to thesemiconductor intermediate electrode.
 3. The film bulk acoustic-waveresonator of claim 2, wherein the cavity is an open cavity implementedby a through-hole penetrating the substrate along a direction from thebottom surface of the substrate to the top surface of the substrate forexposing a bottom surface of the bottom electrode.
 4. The film bulkacoustic-wave resonator of claim 2, wherein the cavity is a closedcavity implemented by a groove dug at a top surface of and in thesubstrate.
 5. A method for manufacturing a film bulk acoustic-waveresonator, comprising: forming a semiconductor intermediate electrode ona semiconductor substrate, the semiconductor intermediate electrodehaving a lower resistivity than the semiconductor substrate; stacking ametallic film for forming a bottom electrode on the entire surface ofthe semiconductor substrate so as to include the semiconductorintermediate electrode; stacking a piezoelectric dielectric film on theentire surface of the bottom electrode and on the semiconductorintermediate electrode; delineating the piezoelectric dielectric filmand the metallic film with an identical etching mask so as to form thepiezoelectric layer and the bottom electrode, the piezoelectric layerhas a same shape and a same size as the bottom electrode in a plan view,the bottom electrode is connected to the semiconductor intermediateelectrode; forming a top electrode on the piezoelectric layer; andforming a bottom electrode wiring so as to be connected to thesemiconductor intermediate electrode.